Added authors and changed package's email to a more general solution.

Michael Kuron authored 4 years ago and Markus Holzer committed 4 years ago

and clean up some old xfails

If this line
from setuptools import find_packages, setup
is run after
from distutils.extension import Extension

a wrong Extension class is used

- version has to be obtained from file when no git repo is available
  like in tar-ball distributed by pypi