Class docstring support

[bitprophet]

The old spec introspected class docstrings and allowed one to use them to override the displayed text in the class header, so e.g.:

class CantHaveApostrophesInClassNames:
  "Can't have apostrophes in class names"
  def some_test_here_I_guess(self):
    assert True

would show up as:

Can't have apostrophes in class names

- some test here I guess

instead of:

CantHaveApostrophesInClassNames

- some test here I guess

Pytest-relaxed doesn't have this implemented yet, but it'd be nice, e.g. Invoke's test suite was just ported and has "lost" a handful of headers this way (they show up, but are ugly and/or missing useful information.)