Add arbitrary audio support to speakers (#982)

Speakers can now play arbitrary PCM audio, sampled at 48kHz and with a
resolution of 8 bits. Programs can build up buffers of audio locally,
play it using `speaker.playAudio`, where it is encoded to DFPWM, sent
across the network, decoded, and played on the client.

`speaker.playAudio` may return false when a chunk of audio has been
submitted but not yet sent to the client. In this case, the program
should wait for a speaker_audio_empty event and try again, repeating
until it works.

While the API is a little odd, this gives us fantastic flexibility (we
can play arbitrary streams of audio) while still being resilient in the
presence of server lag (either TPS or on the computer thread).

Some other notes:
 - There is a significant buffer on both the client and server, which
   means that sound take several seconds to finish after playing has
   started. One can force it to be stopped playing with the new
  `speaker.stop` call.

 - This also adds a `cc.audio.dfpwm` module, which allows encoding and
   decoding DFPWM1a audio files.

 - I spent so long writing the documentation for this. Who knows if it'll
   be helpful!

src/main/java/dan200/computercraft/api/peripheral/GenericPeripheral.java

@@ -23,7 +23,7 @@ public interface GenericPeripheral extends GenericSource
      * Get the type of the exposed peripheral.
      *
      * Unlike normal {@link IPeripheral}s, {@link GenericPeripheral} do not have to have a type. By default, the
-     * resulting peripheral uses the resource name of the wrapped {@link TileEntity} (for instance {@literal minecraft:chest}).
+     * resulting peripheral uses the resource name of the wrapped {@link TileEntity} (for instance {@code minecraft:chest}).
      *
      * However, in some cases it may be more appropriate to specify a more readable name. Overriding this method allows
      * you to do so.

src/main/java/dan200/computercraft/api/peripheral/PeripheralType.java

@@ -63,7 +63,7 @@ public final class PeripheralType
      * Create a new non-empty peripheral type with additional traits.
      *
      * @param type            The name of the type.
-     * @param additionalTypes Additional types, or "traits" of this peripheral. For instance, {@literal "inventory"}.
+     * @param additionalTypes Additional types, or "traits" of this peripheral. For instance, {@code "inventory"}.
      * @return The constructed peripheral type.
      */
     public static PeripheralType ofType( @Nonnull String type, Collection<String> additionalTypes )
@@ -76,7 +76,7 @@ public final class PeripheralType
      * Create a new non-empty peripheral type with additional traits.
      *
      * @param type            The name of the type.
-     * @param additionalTypes Additional types, or "traits" of this peripheral. For instance, {@literal "inventory"}.
+     * @param additionalTypes Additional types, or "traits" of this peripheral. For instance, {@code "inventory"}.
      * @return The constructed peripheral type.
      */
     public static PeripheralType ofType( @Nonnull String type, @Nonnull String... additionalTypes )
@@ -88,7 +88,7 @@ public final class PeripheralType
     /**
      * Create a new peripheral type with no primary type but additional traits.
      *
-     * @param additionalTypes Additional types, or "traits" of this peripheral. For instance, {@literal "inventory"}.
+     * @param additionalTypes Additional types, or "traits" of this peripheral. For instance, {@code "inventory"}.
      * @return The constructed peripheral type.
      */
     public static PeripheralType ofAdditional( Collection<String> additionalTypes )
@@ -99,7 +99,7 @@ public final class PeripheralType
     /**
      * Create a new peripheral type with no primary type but additional traits.
      *
-     * @param additionalTypes Additional types, or "traits" of this peripheral. For instance, {@literal "inventory"}.
+     * @param additionalTypes Additional types, or "traits" of this peripheral. For instance, {@code "inventory"}.
      * @return The constructed peripheral type.
      */
     public static PeripheralType ofAdditional( @Nonnull String... additionalTypes )
@@ -108,7 +108,7 @@ public final class PeripheralType
     }
 
     /**
-     * Get the name of this peripheral type. This may be {@literal null}.
+     * Get the name of this peripheral type. This may be {@code null}.
      *
      * @return The type of this peripheral.
      */