Candidate for a 2.0 release.

1) Python 3 support.  For the love of Jesus.
2) Rev all dependencies including Flask and Twilio.
3) Increase app code test coverage to 100%.
4) Add CI for Py2 and 3 with PEP8 and coverage tracking.
5) Migration to tox for testing.
6) Move test utilities out of requirements and into tox.ini.
7) Beef up README.