Added Opus stream support, added volume interface (#1102)

* Added opus stream support, added volume interface

* Remove setImmediate

* Fix weird syntax error

* Most useless commit ever

You're welcome, @PgBiel

* Fix potential memory leak with OpusScript

Emscripten has the tendency to not free resources even when the Opus engine instance has been garbage collected. Thanks to @abalabahaha for pointing this out.

* Typo

* VoiceReceiver.destroy: destroy opus encoder

src/client/voice/receiver/VoiceReceiver.js

@@ -84,7 +84,8 @@ class VoiceReceiver extends EventEmitter {
       stream._push(null);
       this.opusStreams.delete(id);
     }
-    for (const [id] of this.opusEncoders) {
+    for (const [id, encoder] of this.opusEncoders) {
+      encoder.destroy();
       this.opusEncoders.delete(id);
     }
     this.destroyed = true;