Add bare-bones testing setup.

* A tests/ folder contains run.py - which initialises and
  runs the tests - and tests.py, which holds the obvious.
* test_requirements.txt contains packages that are needed
  for local testing.
* A new makefile target ties everything together.
* Currently, there's one test and it fails due to a lack
  of sufficient parameters to the send() method.
  Everything appears to be importing correctly though.