Bespoke gamutmapping

This branch returns the custom gamut mapping techniques which existed in ART 1. These have their own issues, so using LCMS remains the default, as it delivers superior results. Adding these extra methods allows demonstration of certain things for the purposes of our colour science course, plus it also brought a ArCIELch companion data type to ArCIELab, which should have been there all along. It also fixes the compilation and linkage issues which were present on more recent MacOS releases, and removes the date from the copyright notices in the individual source files. Having the date there was idiotic insofar as this needed to be updated every year.