tests: fix py.test integration with setuptools

* Addresses issue when to tests where executed using
  `python setup.py test`.  (closes #17)

Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
tests: pytest.ini support

Co-authored-by: Yoan Blanc <yoan.blanc@cern.ch>
Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>
docs: initial Sphinx support