Add test skeleton and short (5min / 2mb) demo file for tests

I think this is ready.  Demo is just me in a private game taking down a tower (terribly), 5 minute, 2mb.  

The only test so far just tests a basic load of demo.construct().  Next step is to add more meaningful tests.

To run the test(s) you can

1) run the test file directly
`$ python tests/test_demo.py`

or

2) use a testing library (like nose)
`$ nosetests` (auto-discovers any tests)