Port to support both python2 and python3

Kirill, please check this. I've got all tests passed on python3.4, using six, so it should works also on python2.
The only thing is oauth2, which is not yet ported to py3, so, I've used the version from https://github.com/tseaver/python-oauth2/tree/py3-redux  instead

Thanks!

Created while hackaton #ep14boat