Update badges

A few things:

 * Test on Travis CI against Python 2.6, 2.7, 3.2, 3.3, PyPy and PyPy3 (same as Pillow).
 * All passed apart from 2.6, so fixes for 2.6: replace dict comprehension and use unittest2 on 2.6.
 * Add coverage, tests cover 94%!
 * pep8 and pyflakes fixes.

If you want, you can enable Travis CI and Coveralls on your account, both are free. Then you get the badges working.
 * https://travis-ci.org/profile
 * https://coveralls.io/repos/new