Review of improvements to setup.py indicated issues with the
tox.ini.

Packagers sometimes like to use 'python setup.py test'. This
change adjusts setup.py and setup.cfg to allow this to work
with pytest instead of nose. To make things work, the
settings for coverage need to be moved into tox.ini.

A SkipTest in test_config_middleware is changed to its pytest
equivalent.

Establish testing

Bring tox defaults into a reasonable state, removing env
aliases that tox no longer supports.

Set up travis.ci, including using dist: xenial to get python
3.7 support. pypy is only in trusty.

In the process add a .gitignore so ignored files don't get
in the way of doing this work.

fix paste_deploy paster template for python3

Fix string-formatting args when raising LookupError

Previously, this would trigger

 TypeError: not enough arguments for format string

Switch to pytest