setup.py

Summary:
Create a simple setup.py file from the instructions at
https://packaging.python.org/en/latest/distributing.html. The
`package_data` field doesn't seem to like directories, so we need to
walk the paths under `./peru/resources` to include everything.

Right now we're not including anything under third_party. Instead we
pull those in as dependencies from PyPI. Not sure if this is what we'll
do in the long term, but it's nice that it works.

Test Plan:
Ran `python3 setup.py install --user` and confirmed that peru works.
Then `cd tests; python3 -m unittest` to confirm that tests pass against
the installed version.

Reviewers: sean

Differential Revision: https://phabricator.buildinspace.com/D125