New APU emulation code for nemulator

[James]

I've been using Blargg's Nes_Snd_Emu library since 2004 or 2005 (thanks Blargg!) but decided that it was finally time to write my own. I'd appreciate any feedback on how it sounds. A couple of notes:

- Audio is generated at 1.79MHz, low-pass filtered with a 512th order FIR filter, then downsampled to 48kHz. Not as efficient as Blargg's blip buffer library, but only results in a couple % additional CPU utilization (yay SSE).
- Added VRC6 audio support
- Mig-29, FireHawk, etc. are happy with my DMC IRQ timing
- I just switched to Visual Studio 2012, so if it complains about a missing library, download it from Microsoft.

nemulator 3.0

Thanks,
James