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

Just measure coverage for all tox test targets

and don't have to put `tests/` in tox.ini posargs