Build Sphinx docs on travis with 2.7 runs
Execute Sphinx doctests on travis runs
Skip doctests for coloured output

These should fail when output is not a terminal, and forcing colourised output
is no more useful as a test than simply skipping them.
Merge branch 'feat/travis_sphinx'

* feat/travis_sphinx:
  Skip doctests for coloured output
  Execute Sphinx doctests on travis runs
  Build Sphinx docs on travis with 2.7 runs
Remove unused sphinxcontrib-cheeseshop extension
Bump copyright years
0.13.0 released