Setup continuous integration an CircleCI, AppVeyor and Travis

[jcfr]

You could look at what was done here: https://github.com/amueller/word_cloud

[Erotemic]

I do have Travis set up for continuous testing, and I have used AppVeyor in my other projects (https://github.com/Erotemic/ubelt and https://github.com/Erotemic/xdoctest).

I've been meaning to take the time to learn how to do CI deployment of the package, so I'll take a look.