WebAudio: Add early experimental support for AudioWorklets.

Public issue https://github.com/mackron/miniaudio/issues/597.

examples/build/README.md

@@ -15,3 +15,5 @@ If you output WASM it may not work when running the web page locally. To test yo
 like this:
 
     emrun ./bin/simple_playback_sine.html
+
+If you want to see stdout on the command line when running from emrun, add `--emrun` to your emcc command.
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