PhotoFlow optimizations and benchmarks

[houz]

@Carmelo_DrRaw

For me this seems to be overkill… what I actually need with high priority is an optimized, fast implementation of ICC conversion between matrix profiles in relative colorimetric intent, as well as RGB <-> Lab conversions, which cover 99% of the conversions commonly performed during photo editing.

darktable has such code, in git it’s even SSE enabled. You might ping me on IRC so I can guide you to the places where to find the code.