Add SFX and Music support

[JPTIZ]

Scenery

Currently there's no working SFX implementation. There are some tests on a specific branch. For music, #6 will be needed.

Where to start

One could read about sound register in the technical manual to implement a simple API to access them, and then read about Interrupt Control to make audio play using interrupts. With those two, plus DMA transfer, audio frequencies may be transferred to each channel's FIFO and then music should play.

Hints

These may help:

• Sound on the Gameboy Advance - Deku's Tree of Art;
• Audio Programming on the GameBoy Advance Part 1 - gamedev.net;
• Writing a Game Boy Advance Game - reinterpretcast;
• The Audio Advance.