pytest instead of unittest

[lunemec]

I suggest py.test instead of unittest for testing. I've been using pytest for large project for about half a year now and it is much better. And there is still time to switch with only one test :)

[jonathanslenders]

Yes, thanks for the suggestion. py.test is really great.
There are no tests yet in pyvim. But I think I'll use that indeed. (Today I used it in another project.)

[lunemec]

Also, when there are some problems with certain versions of python and virtualenv, this tool comes in handy: https://testrun.org/tox/latest/

It creates virtualenv for each said version and runs tests with given version of python inside that venv. Very nice for version specific problems.

[lunemec]

I changed pytest and fixed tests. Added tox:
#35