Implement the DSP and at least one Audio backend

[jonas-schievink]

Audio isn't fully implemented: The SPC700 co-processor is working so far, but that's required for most ROMs to work at all. It communicates with a DSP, which does the actual Audio generation. Currently, the DSP is stubbed out and only consists of its registers.

Since there's nothing that produces audio, there also is no code to actually open an audio device, so that would have to be implemented as well to make it work.

Resources

• http://fdwr.tripod.com/docs/brr.txt - Informations about the BRR format, which is decoded by the DSP
• http://wiki.superfamicom.org/snes/show/SPC700+Reference - Contains information on BRR and the DSP registers (scroll down a bit)
• http://problemkaputt.de/fullsnes.htm#snesapudspbrrsamples - Pretty in-depth information about the whole SNES (link goes to the DSP section)

[jonas-schievink]

There's now a cpal backend that should work, so "only" the DSP needs to be implemented.