py-unittest2pytest: updated to 0.4

0.4:
* Add support for assertDictContainsSubset.
* Put parenthesis around expressions if required.
* Fixed assertRaisesRegex, assertRaisesRegexp and assertWarnsRegex.
  The regex was getting replaced with an undefined variable pattern.
* Fix assertRaisesRegex and assertRaisesRegexp with **kwargs and
  atom parameters.
* Made assertRaisesRegex, assertRaisesRegexp and assertWarnsRegex use
  the match kwarg in pytest.raises instead of creating a variable
  with the context manager and doing an assert on re.search.
* Add a short developer guide.
* Remove testing on Python 3.0, 3.1, 3.2, add 3.6 and 3.7.
* Distribute package as a universal wheel.

(adam)