Add Python 3 support and test on Travis CI

[hugovk]

Please enable Travis CI for this repo at https://travis-ci.org/profile/

See .travis.yml for what it does: some static analysis and then does a test run of python generate.py.

Here's an example build: https://travis-ci.org/hugovk/pythonwheels/builds/283534796

[meshy]

@hugovk thank you for this!

I hope you don't mind if I ask for a few alterations:

• It's a great idea to move this to python 3. I don't think there's much need to support python 2 at the same time, however. Would you mind removing it?
• Instead of pyflakes and pep8 separately, could you please use flake8?

Once again, this is much appreciated. Thank you!

[meshy]

Oh, I should mention: I've now enabled TravisCI for this project, as you requested.

[hugovk]

Updated!

[hugovk]

@ghickman Thanks, both updated.

[hugovk]

@meshy Updated!

[meshy]

You're a star! Thank you!