Improve Web Audio buffering.

This changes the Web Audio code to increase buffers according to
SDL.audio.numSimultaneouslyQueuedBuffers, which can be changed via
Module['SDL_numSimultaneouslyQueuedBuffers']. It becomes more
similar to Mozilla Audio Data code. Multiple pending timers are
used to improve sound when there is high CPU usage.
Add myself to AUTHORS.
Merge pull request #2097 from dreamlayers/web_audio

Web Audio buffering improvement