High quality resampler

Think of this as rough draft. Taking suggestions to make it robust, error free, and prettier!

For more information:
https://docs.google.com/document/d/1tBEgsJh7QiwNwepXI0eobfK3U8LkJButSyeuFt1degM/edit?usp=sharing

removed: SSE includes

added: 16bit -> float -> 16bit functions
added: linear interpolator and high-quality interpolator functions (including Resampler class)
added: dithering

changed: renamed variables and reformatted a few things to fit with style guide
changed: use s16, u16, s32, u32 etc
changed: store samples and do all computations as floats
changed: volume from 0 - 255
That's how MatrixMath.h and DPL2Decode.cpp do it. I tried:

#define _USE_MATH_DEFINES
#include <cmath>

at the very top of the Mixer.cpp file, but it did not compile on my VS 2013, saying M_PI isn't defined or something. I've read that it must be precompiled headers, or other includes before it, but if I put it at the top of the file, should be before any other includes anyways. The other option, is we could add it in MathUtil as a static const double or float (or have one for each), and then we won't have to use M_PI. I dunno, suggestions?