Enable Travis CI continous automated testing

We will develop Rules for Drupal 8 at https://github.com/fago/rules (mirrored to drupal.org) and we want to enable Travis CI for automated testing.

I have committed a .travis.yml file which runs the PHPUnit tests and also installs Drupal core to run the Simpletest integration tests. Build results of my Rules fork: https://travis-ci.org/klausi/rules

Now the only thing left to do is for fago to enable this on the main fago/rules repository, since I don't seem to have permission to do that. See http://docs.travis-ci.com/user/getting-started/ for the steps signup your repository.