Release to pypi on tag

Fixes #366 
> How was this encrypted? (Just for my FYI.)

If you are lazy like me, you can use a sort of conf wizard by executing `travis setup pypi`. This will ask you some questions and add stuff to your `travis.yml`.
If you're just interested in encrypting a var, `travis encrypt SOMEVAR=secretvalue` will output the `secure: ".... encrypted data ...."` that you can add to your `.travis.yml`.

> Also, is this preferred to using the secured environment variables?
I thought in this case it's fine if it's in the `.travis.yml` because the only reason to change this would be if you wanted to deploy a package, at which point you should change a bunch of other stuff.
Having the other environment variables allows users to run the regression tests and such withouth having to change files on their fork.
WDYT?