Add deployment to PyPI using Travis

[nicoddemus]

trafficstars

Here's how pytest does it: https://github.com/pytest-dev/pytest/blob/a4c426b1a891a22ae1b63d0a0fa2dcdf690e69db/.travis.yml#L61-L75

[altendky]

I did a deploy stage in one of my projects. I also started a little twine-on-tags script that'd be cross-ci/platform and I could make use of versioneer to detect version tags (I assume) so I might go that route.

Thanks for the reference.