added travis continuous integration

[edsu]

These are small changes to get tests running with travis-ci whenever you push to the repository. Once setup on travis-ci you should get nice email notifications when tests fail, and reports like this.

If you decide to use this pull request you'll want to s/edsu/cygri/ in the README.md so those links point at your repository.

If you are new to travis-ci.org let me know and I can give you instructions for getting started with it, but I imagine you can figure it out quickly. Basically just go to https://travis-ci.org/profile log in and turn on your htmldiff repository.

The tests are currently failing as indicated in #1