Some changes to Lua machines and string loading

- Share the ILuaContext across all method calls, as well as shifting it
   into an anonymous class.
 - Move the load/loadstring prefixing into bios.lua
 - Be less militant in prefixing chunk names:
   - load will no longer do any auto-prefixing.
   - loadstring will not prefix when there no chunk name is supplied.
     Before we would do `"=" .. supplied_program`, which made no sense.

src/main/java/dan200/computercraft/api/lua/ILuaContext.java

@@ -32,7 +32,11 @@ public interface ILuaContext
      *                              intercepted, or the computer will leak memory and end up in a broken state.
      */
     @Nonnull
-    Object[] pullEvent( @Nullable String filter ) throws LuaException, InterruptedException;
+    default Object[] pullEvent( @Nullable String filter ) throws LuaException, InterruptedException {
+        Object[] results = pullEventRaw( filter );
+        if( results.length >= 1 && results[0].equals( "terminate" ) ) throw new LuaException( "Terminated", 0 );
+        return results;
+    }
 
     /**
      * The same as {@link #pullEvent(String)}, except "terminated" events are ignored. Only use this if you want to
@@ -47,7 +51,9 @@ public interface ILuaContext
      * @see #pullEvent(String)
      */
     @Nonnull
-    Object[] pullEventRaw( @Nullable String filter ) throws InterruptedException;
+    default Object[] pullEventRaw( @Nullable String filter ) throws InterruptedException {
+        return yield( new Object[] { filter } );
+    }
 
     /**
      * Yield the current coroutine with some arguments until it is resumed. This method is exactly equivalent to