Tests setup

This pull request introduces basic tests setup: [tox](https://tox.readthedocs.org) running [nosetests](http://nose.readthedocs.org) against both Python 2.6 and Python 2.7 virtualenvs (this is what we want to support, right?), as well as [pylint](http://www.pylint.org/) for checking code style and a nice static analysis.

And for the reference, I was roughly following what other popularprojects, such as https://github.com/Pylons/pyramid or https://github.com/Pylons/substanced, do for testing.