add tox.ini config file for 'tox' tool
add tox.ini config file for 'tox' tool

Tox allows to automatically run tests in isolated virtual environments on multiple python versions,
both locally and on the continuous integration servers.

Read more at Tox documentation http://tox.readthedocs.io/

moyogo/mutatormath,LettError/MutatorMath,anthrotype/MutatorMath