Utilise @Mod.EventBusSubscriber a little more

This offers several advantages

 - Less registration code: the subscribers are reigstered automatically,
   and we don't need to worry about sided-proxies.
 - We no longer have so many .instance() calls.

src/main/java/dan200/computercraft/shared/proxy/CCTurtleProxyCommon.java

@@ -21,38 +21,23 @@ import dan200.computercraft.shared.turtle.items.ItemTurtleLegacy;
 import dan200.computercraft.shared.turtle.items.ItemTurtleNormal;
 import dan200.computercraft.shared.turtle.items.TurtleItemFactory;
 import dan200.computercraft.shared.turtle.upgrades.*;
-import dan200.computercraft.shared.util.DropConsumer;
 import dan200.computercraft.shared.util.ImpostorRecipe;
 import net.minecraft.block.Block;
-import net.minecraft.entity.Entity;
 import net.minecraft.init.Items;
 import net.minecraft.item.Item;
 import net.minecraft.item.ItemStack;
 import net.minecraft.item.crafting.IRecipe;
 import net.minecraft.util.ResourceLocation;
-import net.minecraft.util.math.AxisAlignedBB;
-import net.minecraft.util.math.BlockPos;
-import net.minecraft.world.World;
 import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.event.RegistryEvent;
+import net.minecraftforge.fml.common.Mod;
 import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
 import net.minecraftforge.fml.common.registry.EntityRegistry;
 import net.minecraftforge.fml.common.registry.GameRegistry;
 import net.minecraftforge.registries.IForgeRegistry;
 
-import java.lang.ref.WeakReference;
-import java.util.List;
-import java.util.function.Function;
-
 public abstract class CCTurtleProxyCommon implements ICCTurtleProxy
 {
-    private Function<ItemStack, ItemStack> dropConsumer;
-    private List<ItemStack> remainingDrops;
-    private WeakReference<World> dropWorld;
-    private BlockPos dropPos;
-    private AxisAlignedBB dropBounds;
-    private WeakReference<Entity> dropEntity;
-
     @Override
     public void preInit()
     {
@@ -67,7 +52,6 @@ public abstract class CCTurtleProxyCommon implements ICCTurtleProxy
     @Override
     public void init()
     {
-        registerForgeHandlers();
         registerTileEntities();
     }
 
@@ -248,16 +232,11 @@ public abstract class CCTurtleProxyCommon implements ICCTurtleProxy
         GameRegistry.registerTileEntity( TileTurtleAdvanced.class, new ResourceLocation( ComputerCraft.MOD_ID, "turtleadv" ) );
     }
 
-    private void registerForgeHandlers()
-    {
-        MinecraftForge.EVENT_BUS.register( new ForgeHandlers() );
-        MinecraftForge.EVENT_BUS.register( DropConsumer.instance() );
-    }
-
-    private class ForgeHandlers
+    @Mod.EventBusSubscriber( modid = ComputerCraft.MOD_ID )
+    public static class ForgeHandlers
     {
         @SubscribeEvent
-        public void onTurtleAction( TurtleActionEvent event )
+        public static void onTurtleAction( TurtleActionEvent event )
         {
             if( ComputerCraft.turtleDisabledActions.contains( event.getAction() ) )
             {

src/main/java/dan200/computercraft/shared/proxy/ComputerCraftProxyCommon.java

@@ -85,10 +85,10 @@ import net.minecraft.world.World;
 import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.event.RegistryEvent;
 import net.minecraftforge.event.entity.player.PlayerContainerEvent;
-import net.minecraftforge.event.world.WorldEvent;
 import net.minecraftforge.fml.client.event.ConfigChangedEvent;
 import net.minecraftforge.fml.common.FMLCommonHandler;
 import net.minecraftforge.fml.common.Loader;
+import net.minecraftforge.fml.common.Mod;
 import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
 import net.minecraftforge.fml.common.gameevent.TickEvent;
 import net.minecraftforge.fml.common.network.FMLNetworkEvent;
@@ -371,9 +371,7 @@ public abstract class ComputerCraftProxyCommon implements IComputerCraftProxy
 
     private void registerForgeHandlers()
     {
-        ForgeHandlers handlers = new ForgeHandlers();
-        MinecraftForge.EVENT_BUS.register( handlers );
-        NetworkRegistry.INSTANCE.registerGuiHandler( ComputerCraft.instance, handlers );
+        NetworkRegistry.INSTANCE.registerGuiHandler( ComputerCraft.instance, new GuiHandler() );
     }
 
     private void registerNetwork()
@@ -421,14 +419,12 @@ public abstract class ComputerCraftProxyCommon implements IComputerCraftProxy
             showTableClient( packet.getTable() ) );
     }
 
-    public class ForgeHandlers implements IGuiHandler
+    public class GuiHandler implements IGuiHandler
     {
-        private ForgeHandlers()
+        private GuiHandler()
         {
         }
 
-        // IGuiHandler implementation
-
         @Override
         public Object getServerGuiElement( int id, EntityPlayer player, World world, int x, int y, int z )
         {
@@ -561,23 +557,29 @@ public abstract class ComputerCraftProxyCommon implements IComputerCraftProxy
                     return null;
             }
         }
+    }
 
-        // Event handlers
+    @Mod.EventBusSubscriber( modid = ComputerCraft.MOD_ID )
+    public final static class ForgeHandlers
+    {
+        private ForgeHandlers()
+        {
+        }
 
         @SubscribeEvent
-        public void onConnectionOpened( FMLNetworkEvent.ClientConnectedToServerEvent event )
+        public static void onConnectionOpened( FMLNetworkEvent.ClientConnectedToServerEvent event )
         {
             ComputerCraft.clientComputerRegistry.reset();
         }
 
         @SubscribeEvent
-        public void onConnectionClosed( FMLNetworkEvent.ClientDisconnectionFromServerEvent event )
+        public static void onConnectionClosed( FMLNetworkEvent.ClientDisconnectionFromServerEvent event )
         {
             ComputerCraft.clientComputerRegistry.reset();
         }
 
         @SubscribeEvent
-        public void onClientTick( TickEvent.ClientTickEvent event )
+        public static void onClientTick( TickEvent.ClientTickEvent event )
         {
             if( event.phase == TickEvent.Phase.START )
             {
@@ -586,7 +588,7 @@ public abstract class ComputerCraftProxyCommon implements IComputerCraftProxy
         }
 
         @SubscribeEvent
-        public void onServerTick( TickEvent.ServerTickEvent event )
+        public static void onServerTick( TickEvent.ServerTickEvent event )
         {
             if( event.phase == TickEvent.Phase.START )
             {
@@ -596,23 +598,13 @@ public abstract class ComputerCraftProxyCommon implements IComputerCraftProxy
         }
 
         @SubscribeEvent
-        public void onWorldLoad( WorldEvent.Load event )
-        {
-        }
-
-        @SubscribeEvent
-        public void onWorldUnload( WorldEvent.Unload event )
-        {
-        }
-
-        @SubscribeEvent
-        public void onConfigChanged( ConfigChangedEvent.OnConfigChangedEvent event )
+        public static void onConfigChanged( ConfigChangedEvent.OnConfigChangedEvent event )
         {
             if( event.getModID().equals( ComputerCraft.MOD_ID ) ) Config.sync();
         }
 
         @SubscribeEvent
-        public void onContainerOpen( PlayerContainerEvent.Open event )
+        public static void onContainerOpen( PlayerContainerEvent.Open event )
         {
             // If we're opening a computer container then broadcast the terminal state
             Container container = event.getContainer();

src/main/java/dan200/computercraft/shared/turtle/core/TurtlePlaceCommand.java

@@ -226,7 +226,7 @@ public class TurtlePlaceCommand implements ITurtleCommand
         // Start claiming entity drops
         Entity hitEntity = hit.getKey();
         Vec3d hitPos = hit.getValue();
-        DropConsumer.instance().set(
+        DropConsumer.set(
             hitEntity,
             drop -> InventoryUtil.storeItems( drop, turtle.getItemHandler(), turtle.getSelectedSlot() )
         );
@@ -266,7 +266,7 @@ public class TurtlePlaceCommand implements ITurtleCommand
         }
 
         // Stop claiming drops
-        List<ItemStack> remainingDrops = DropConsumer.instance().clear();
+        List<ItemStack> remainingDrops = DropConsumer.clear();
         for( ItemStack remaining : remainingDrops )
         {
             WorldUtil.dropItemStack( remaining, world, position, turtle.getDirection().getOpposite() );

src/main/java/dan200/computercraft/shared/turtle/upgrades/TurtleTool.java

@@ -135,7 +135,7 @@ public class TurtleTool extends AbstractTurtleUpgrade
             }
 
             // Start claiming entity drops
-            DropConsumer.instance().set( hitEntity, turtleDropConsumer( turtle ) );
+            DropConsumer.set( hitEntity, turtleDropConsumer( turtle ) );
 
             // Attack the entity
             boolean attacked = false;
@@ -225,7 +225,7 @@ public class TurtleTool extends AbstractTurtleUpgrade
         }
 
         // Consume the items the block drops
-        DropConsumer.instance().set( world, blockPosition, turtleDropConsumer( turtle ) );
+        DropConsumer.set( world, blockPosition, turtleDropConsumer( turtle ) );
 
         TileEntity tile = world.getTileEntity( blockPosition );
 
@@ -257,7 +257,7 @@ public class TurtleTool extends AbstractTurtleUpgrade
 
     private void stopConsuming( ITurtleAccess turtle )
     {
-        List<ItemStack> extra = DropConsumer.instance().clear();
+        List<ItemStack> extra = DropConsumer.clear();
         for( ItemStack remainder : extra )
         {
             WorldUtil.dropItemStack( remainder, turtle.getWorld(), turtle.getPosition(), turtle.getDirection().getOpposite() );

src/main/java/dan200/computercraft/shared/util/DropConsumer.java

@@ -6,6 +6,7 @@
 
 package dan200.computercraft.shared.util;
 
+import dan200.computercraft.ComputerCraft;
 import net.minecraft.entity.Entity;
 import net.minecraft.entity.item.EntityItem;
 import net.minecraft.item.ItemStack;
@@ -15,6 +16,7 @@ import net.minecraft.world.World;
 import net.minecraftforge.event.entity.EntityJoinWorldEvent;
 import net.minecraftforge.event.entity.living.LivingDropsEvent;
 import net.minecraftforge.event.world.BlockEvent;
+import net.minecraftforge.fml.common.Mod;
 import net.minecraftforge.fml.common.eventhandler.EventPriority;
 import net.minecraftforge.fml.common.eventhandler.SubscribeEvent;
 
@@ -23,23 +25,21 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.function.Function;
 
-public class DropConsumer
+@Mod.EventBusSubscriber( modid = ComputerCraft.MOD_ID )
+public final class DropConsumer
 {
-    private static final DropConsumer instance = new DropConsumer();
-
-    public static DropConsumer instance()
+    private DropConsumer()
     {
-        return instance;
     }
 
-    private Function<ItemStack, ItemStack> dropConsumer;
-    private List<ItemStack> remainingDrops;
-    private WeakReference<World> dropWorld;
-    private BlockPos dropPos;
-    private AxisAlignedBB dropBounds;
-    private WeakReference<Entity> dropEntity;
+    private static Function<ItemStack, ItemStack> dropConsumer;
+    private static List<ItemStack> remainingDrops;
+    private static WeakReference<World> dropWorld;
+    private static BlockPos dropPos;
+    private static AxisAlignedBB dropBounds;
+    private static WeakReference<Entity> dropEntity;
 
-    public void set( Entity entity, Function<ItemStack, ItemStack> consumer )
+    public static void set( Entity entity, Function<ItemStack, ItemStack> consumer )
     {
         dropConsumer = consumer;
         remainingDrops = new ArrayList<>();
@@ -51,7 +51,7 @@ public class DropConsumer
         entity.captureDrops = true;
     }
 
-    public void set( World world, BlockPos pos, Function<ItemStack, ItemStack> consumer )
+    public static void set( World world, BlockPos pos, Function<ItemStack, ItemStack> consumer )
     {
         dropConsumer = consumer;
         remainingDrops = new ArrayList<>();
@@ -61,7 +61,7 @@ public class DropConsumer
         dropBounds = new AxisAlignedBB( pos ).grow( 2, 2, 2 );
     }
 
-    public List<ItemStack> clear()
+    public static List<ItemStack> clear()
     {
         if( dropEntity != null )
         {
@@ -89,14 +89,14 @@ public class DropConsumer
         return remainingStacks;
     }
 
-    private void handleDrops( ItemStack stack )
+    private static void handleDrops( ItemStack stack )
     {
         ItemStack remaining = dropConsumer.apply( stack );
         if( !remaining.isEmpty() ) remainingDrops.add( remaining );
     }
 
     @SubscribeEvent( priority = EventPriority.LOWEST )
-    public void onEntityLivingDrops( LivingDropsEvent event )
+    public static void onEntityLivingDrops( LivingDropsEvent event )
     {
         // Capture any mob drops for the current entity
         if( dropEntity != null && event.getEntity() == dropEntity.get() )
@@ -108,7 +108,7 @@ public class DropConsumer
     }
 
     @SubscribeEvent( priority = EventPriority.LOWEST )
-    public void onHarvestDrops( BlockEvent.HarvestDropsEvent event )
+    public static void onHarvestDrops( BlockEvent.HarvestDropsEvent event )
     {
         // Capture block drops for the current entity
         if( dropWorld != null && dropWorld.get() == event.getWorld()
@@ -123,7 +123,7 @@ public class DropConsumer
     }
 
     @SubscribeEvent( priority = EventPriority.LOWEST )
-    public void onEntitySpawn( EntityJoinWorldEvent event )
+    public static void onEntitySpawn( EntityJoinWorldEvent event )
     {
         // Capture any nearby item spawns
         if( dropWorld != null && dropWorld.get() == event.getWorld() && event.getEntity() instanceof EntityItem