Convert colors using ICC profiles to sRGB with support for v2 and v4 ICC color
profiles, black point correction and gamut compression.

This code was originally based on code from two other projects,
https://github.com/mandykoh/prism (mainly image file format parsing, MIT license)
and http://github.com/go-andiamo/iccarus (mainly ICC file parsing, Apache 2.0
license). However it is extensively modified and bears little resemblance to
either project's code anymore.
