CI and stuff

A few bits 'n' pieces:

 * Add Travis CI and Coveralls coverage. They're free for open source, you'll need to enable them first for the main repo, and you get a report like this: https://travis-ci.org/hugovk/spotipy
 * CI does some runs the tests with coverage, and the examples without coverage.
 * The tests pass for Python 2.6, 2.7, 3.3 and PyPy. Python 3.2 fails because it doesn't have `u'sometext'`, but I guess most would just use 3.3. Python 3.4 errors because Travis hasn't added 3.4 yet, but it'll be there [any day now](https://github.com/travis-ci/travis-ci/issues/1989#issuecomment-39315535).
 * CI does some pep8 and pyflakes static analysis at the end.
 * Some pep8 and pyflakes clean-up, and made examples run on all versions.
 * Coveralls reports looks like this: https://coveralls.io/builds/658728 Could be adjusted to exclude tests.py and to show actual spotipy.py source, but you get the idea.