Python 3 support, dropped python 2.5 support

Minor fixes for pep8 sake, removed deprecated assert_
travis.yml
More pep8 fixes
Travis doesn't support 3.1

https://github.com/travis-ci/travis-ci.github.com/pull/157#issuecomment-10632254
Absolute imports
Merge pull request #13 from coagulant/py3k

Python 3 support