Proposal: completely switch to py.test

[funkyfuture]

this tools has been released recently: https://github.com/dropbox/unittest2pytest

if it does its job good, it shouldn't be such an effort to rewrite all tests as they are usable with pytest.

i'd be much in favor for it, alone for the heavily reduced char count of the tests.py. but certainly after an 1.0 release.

[nicolaiarocci]

Interesting.

[funkyfuture]

just two cents:

• used it. it's realiable. it's not without straight forward effort nonetheless. but a good start.
• pytest doesn't run on pyston yet.

[nicolaiarocci]

Partially addressed by #259