Add APU Emulator

[bonimy]

Issue

SnesXM needs an APU (audio processing unit) emulator.

Features

I don't know a lot about sound emulation, but obviously it's an essential component of SNES emulation.

Resolution

Port APU code from snes9x. Note that the Blargg files are just for environment configuration. They aren't needed in the C# environment.

Task List

• - Dsp
• - SpcDsp
• - Smp
• - SmpState
• - ApuEmulator
• - HermiteResampler
• - Msu1
• - Resampler
• - RingBuffer