Import py-tox-2.1.1 as devel/py-tox.

Tox is a generic virtualenv management and test command line tool
you can use for:

* checking your package installs correctly with different Python
  versions and interpreters
* running your tests in each of the environments, configuring your
  test tool of choice
* acting as a frontend to Continuous Integration servers, greatly
  reducing boilerplate and merging CI and shell-based testing.

(wiz)