fix: dev: added inequality method (fixes #26)

[tommilligan]

This fixes issue #26 where checking if two Color objects were not equal (using !=) always returned True.

PR includes tests. I don't think additional changes to documentation are required.

This PR is based on the master branch, as the dev branch is currently failing build for Python 3.4.

[coveralls]

Coverage decreased (-0.4%) to 98.729% when pulling 6f9167a on tommilligan:master into 69f5add on vaab:master.

[coveralls]

Coverage decreased (-0.4%) to 98.729% when pulling 6f9167a on tommilligan:master into 69f5add on vaab:master.

[tommilligan]

Root cause was that the Color class already has a custom __eq__ method, but no custom __ne__ method.

This PR:

• implements the __ne__ method
• refactors the __eq__ method
• adds relevant doctests

[vaab]

Ok, many thanks. I'm in the process of reviewing your code and going into the #25 cases you've brought up.
As a first notice, I'm not very keen upon adding this _is_comparable(..) method, and I'll look into enforcing python 3 default behavior as I understand it (which should be to use not ==).

I have posted another PR #29, feel free to comment !

[vaab]

I pushed the other PR #29 that tackle the same issue a little differently. If anything is wrong with that, please voice your concern.
Thanks !