Use tox as a test environment manager.
Review Request #11914 — Created Jan. 9, 2022 and submitted
kgb needs to be regularly tested with many different versions of Python.
To faciliate this,
toxcan now be used.
tox, environments will be set up for Python 2.7, 3.6-3.10,
and PyPy 3.7/3.8. Tests will then be run. This allows for rapid feedback
on whether changes to kgb work or break some supported version of
tox. All tests passed.