ENH: Add Travis

Travis builds pass, see:

https://travis-ci.org/Eric89GXL/PySurfer/builds/18242751

Someone with admin privileges on `PySurfer` will have to activate the service hook for it to work, and probably also configure something on `coveralls.io`.

Getting Travis to work required moving the `example_data` (~2.8 MB) into the package (as `surfer/data`), which I think is a welcome change anyway. I also changed a few `pep8` issues.

Also, the `fsaverage_min.tar.gz` file is currently hosted on my space at UW, which is *not* a tenable long-term solution. @mwaskom do you have somewhere you could host it? If not, @agramfort would it be possible to upload it to Martino's space somewhere? It's <30MB.