Add sound sample generator

[tannewt]

It should generate a note based on a set of variables. See these for ideas:

Gameboy: https://youtu.be/HyzD8pNlpwI?t=24m10s
Pico-8: https://www.youtube.com/watch?v=Wj1LJQutMCY
bfxr: https://github.com/increpare/bfxr

[ladyada]

@tannewt i think synthio is basically this? we can close :)