Merge pull request #3 from yoavweiss/master

Work around for out-of-bounds read
Lowercase type names
Updated rwpng.h from pngquant
makefile for libpng16
Formatting
Refactored dssim.c to allow multiple comparisons at once
Refactored main.c to allow multiple comparisons at once
Updated readme
Use mininum of averages rather than average of minimums

Improves tid2008 score in all categories except noise
Simpler dealloc
Improved LAB conversion for values < epsilon
Gamma LUT
debug
Numeric optimization in Lab conversion
Removed unused function
Don't compute SSIM for alpha channel separately

since it's indirectly included in the blended opaque channels
Avoid unnecessary blending
Optimized blur
Return map as float array
Process channels one after another