Travis CI integration

Allow continuous integration (CI) via Travis CI: after each commit and for each (updated) pull request a new build is triggered and the unit tests are run.

Follow these simple steps to enable the GIT trigger for Travis CI from Github: http://about.travis-ci.org/docs/user/getting-started/

After that you can add this line somewhere near the top of your README.md file to get a fast visual feedback about the current build status:
`[![Build Status](https://travis-ci.org/unclebob/fitnesse.png)](https://travis-ci.org/unclebob/fitnesse) Travis CI build status`
resolves to this link within the Github environment:
[![Build Status](https://travis-ci.org/unclebob/fitnesse.png)](https://travis-ci.org/unclebob/fitnesse) Travis CI build status

And you get information about the build status indicated directly at the top of each pull request.