PR: Implement "colour.chromatic_adaptation" convenient definition that transforms "CIE XYZ" tristimulus values from one viewing condition to another.

References #123.
(Nitpicking level: extreme) This slightly deviates from the [numpy documentation standard for parameters that only can assume fixed values] (https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt#sections). (Curly braces and default value first in sequence)