fix compile
Skip zero-coefficient contributors, a fairly decent speedup.
Merge branch 'resample' of http://github.com/bsvino/stb into resample
compile as C;
fix some unsigned/signed comparisons;
avoid round() since it's not in pre-C99 C;
remove MAX_CHANNELS since I never ended up needing it;
rename STBIR_EPSILON to STBIR_ALPHA_EPSILON;
don't use STBIR_ALPHA_EPSILON on float input (can't remove it properly due to numeric precision, and they can do it themselves);
optimize subtraction of STBIR_ALPHA_EPSILON;
sorry i forgot to commit these separately!;
fix stbir__linear_to_srgb_uchar:
    1. table stored threshhold of transition from i to i+1, but wants to be i-1 to i
    2. table was computed by dividing uchar by 256.0 instead of 255.0, causing it to be 100% wrong
update with new tests for srgb conversion
Documentation;
rename STBIR_FLAG_PREMULTIPLED_ALPHA to STBIR_FLAG_ALPHA_PREMULTIPLIED so that both flags have "ALPHA" first
Optimizations: Skip zero-coefficient contributions. Reduce the size of the coefficients array when downsampling.
Merge remote-tracking branch 'remotes/nothings/resample' into resample