Add some unit tests

[peterbrittain]

It's about time this project had some automated tests. Things to consider are:

• Python 2 / 3
• Basic functional paths for low level API
• More detailed tests of higher level API - e.g. widget logic
• Support for keyboard input injection (for better testing)

Probably should use https://travis-ci.org for the tests.

[peterbrittain]

Started experimenting... looks like coveralls output would be good too. Now just need to get a LOT more coverage.

[peterbrittain]

Also would be helpful if I could inject input into the test system. Looks like this is possible on curses and win32. Not sure if it's worth the reverse translation effort, though. Maybe I should just use an internal buffer (and flag the buffer for testing only, rather than genuine OS event injection)?

[peterbrittain]

Would be nice to get Windows and Linux coverage... Looks like I might have to use https://github.com/Robpol86/appveyor-artifacts to get it all into coveralls.

[peterbrittain]

Travis and appveyor integration now done. Code coverage getting there for non visual interfaces. Need to think about all the genuinely visual tests and where to draw the line for UT.

[peterbrittain]

OK - all major issues resolved. Some tests are less than perfect as it is crazily expensive to test randomized visual content and the low-level interactions with the OS terminal/console. Nonetheless most lines are now basically covered, so crass regressions should be caught (and genuine failures of purely visual content will be easily spotted by eye). Now closing.