Adding tox to test with several python interpreters

Hello there,

I just forked your very usefull Wikipedia repos and made some changes in the management of unit tests by:
* using `nose2` to find and run tests
* using `tox` to test in a separate environment for several interpreters (2.7, 3.3, 3.4)

I also fixed some pep8 issues with `autopep8` (the last commit: 1452676). Maybe you can ignore this one since it's just style.

If you think that would be useful, don't hesitate to pull the change.

Thank you for your great work
Rémi