TST add travis

Adds travis ci, see http://about.travis-ci.org/docs/user/getting-started/

*[jinja2](https://github.com/mitsuhiko/jinja2) doesn't support 3.1 or 3.2 (it uses u'' syntax) so these builds are not included (the tests fail!).*

Also, numpy is currently a hard dependency in the tests, however some tests should probably skip if numpy is not available (so this case can be tested).