Use pytest for running tests

[jaraco@…]

I'm working on a branch to support a unified codebase for Python 2 and 3 (​https://github.com/jaraco/genshi/tree/feature/py3-native). One problem I'm up against is the doctests failing thus:

File "/Users/jaraco/Dropbox/code/public/genshi/genshi/util.py", line 207, in genshi.util.stripentities
Failed example:
    stripentities('1 < 2 …', keepxmlentities=True)
Expected:
    u'1 < 2 …'
Got:
    '1 < 2 …'

Pytest has a solution for this (​https://docs.pytest.org/en/latest/doctest.html), a plugin for doctest that allows unicode to match even on Python 2 where the 'u' prefixes text strings.

Pytest also brings lots of nice features for test discovery, fixtures, and other nice features.

Could Genshi adopt pytest as its test runner?