REF: Support Python 3 using six.

CLN: Style fixes

CLN: Revert back to relative imports.

Fix py3 issue in plots
BLD: Use skimage for all builds instead of PIL.
BLD: Remove libtiff, which is not in setup.py and not py3 compat.
BLD: Remove print statement from build.
Merge pull request #122 from soft-matter/py3

REF: Support Python 3 using six.