Make tests runnable with pytest.

[jd-boyd]

Also update travisci to use pytest.

This is a start on issue #23.

[jd-boyd]

The idea is to get the existing tests runnable with pytest and travis running it in place before adding to the test load.

I saw the previous failure. Python 2.7 support should be fixable, which I will work on. Python 3.2 and 3.3 is more of a probablem since they aren't supported by pytest. thus removing them from the automatic running.

[jd-boyd]

BTW, here is the way to see test coverage:

pytest --cov-report term-missing --cov=HowLong