set up tox

[nabicht]

This makes it easier to run tests in multiple virtual environments.

When setting this up also make sure i have a virtual env for at least:

1. 3.6
2. 2.7

Dependent on #67

[aggmoulik]

You don't have any setup.py file for the tox implementation.

[nabicht]

Agreed. I don’t have a setup.py file (yet). I will. This is really dependent on that task. Issue editors to reflect dependency. Thanks!