get rid of PEP8 errors about private module functions
tox: check setup.py too
tox: create dedicated environments for pep8 and pyflakes
pytest: add setup.cfg with ignore cmdline option
tox: remove unnecessary install command
tox: add py3 environment
tox: save coverate and JUnit reports
Ignore build output from tox
Merge pull request #13 from pkit/pty_private

pep8: fix errors about using private module functions
Merge pull request #14 from mgeisler/tox

tox: align file with tox.in in zpm repo