Eliminate separate F16C CPU type and move routines under AVX2 family
Change OrderedDither to use a fixed number of offsets
Replace usage of std::bind with lambda functions
Move make_integer_to_float and make_float_to_integer helpers into quantize.h
Add SSE2 version of DepthConvert and OrderedDither

Up to 300% speedup in half_to_float and float_to_half.
Up to 800% speedup in ordered dither.