Support for Python3 and Django 1.7

Hi,

I added Python 3 support in libthumbor using six. Tests should pass for Python 2.7 and 3.4.
I know it's suboptimal, but right now, Thumbor doesn't support Python 3, so to pass the unit tests in Python 3.4, I also ported the url and crypto modules from Thumbor and added them to the test directory.
Finally, I modified the setup script to add the six dependency.

Hope you find it useful.