Skip zero-coefficient contributors, a fairly decent speedup.
Optimizations: Skip zero-coefficient contributions. Reduce the size of the coefficients array when downsampling.
Merge remote-tracking branch 'remotes/nothings/resample' into resample
Calculate and store vertical contributors first so that they can be normalized and optimized.
Merge branch 'resample' of http://github.com/bsvino/stb into resample
tweak docs; fix compile error in UNUSED_PARAM stuff
checkboard test to verify srgb
rename filters, document them