SMS audio

This past weekend, I decided to switch priorities and spent some time working on SMS audio. As it turns out, implementing the SN76489 chip was not as difficult as what I originally imagined. The tone and noise channels seem to be working correctly, meaning that a bunch of games are now fully playable including sound! Last time I worked on audio (for the GB PAPU), I remember the overall experience being quite complex, but that was mainly due to the audio resampling algorithms which were developed from scratch (they are now part of the framework). Now is the time for cleanup and integration.