Update various docstrings.
Update docstrings in "ATD95" color appearance model.
Implement support for "CMCCAT2000" chromatic adaptation model.

References #120.
Add "optional" descriptor to parameters docstrings.
Implement support for "CMCCAT2000" chromatic adaptation model.

References #120.
Use consistent data in "colour.adaptation.tests.tests_cmcat2000" module unit tests.
Merge branch 'feature/CMCCAT2000' of https://github.com/colour-science/colour into feature/CMCCAT2000