tox.ini refactor
Add persei dependency to tox..ini
Change all py2and3 references to persei
Remove py2and3
Remove py2and3 tests. TODO: move it to persei.
Remove py2and3 from util.__init__
Use persei from PyPI in tox.ini
Add persei to setup.py
Merge pull request #132 from iurisilvio/persei

Use persei instead of py2and3