Added support for different illuminants.
Added new tests. The support for a wider range of illuminants is now tested.
Added tests for the new functionality.
Undone change in skimage/__init__.py.
The format strings were updated to include numbers.
Corrected code to conform to Python coding conventions (PEP 8).

Added test code for handling exceptions.

Corrected test code to use the full path to the test data.
Added Stephan comments.

Syntax is now checked using `flake8`.
Removed the print statements from the test code.
Incorporated Stefan's comments.
Added Johannes' comments.
Merge pull request #1130 from capitanbatata/more-illuminants

Add more illuminants to color conversion