Set up Travis CI for SLF4J

DO NOT MERGE WITHOUT READING THE STEPS BELOW:

To complete the setup, please follow (@ceki) these steps:

* Sign into Travis with your github account at http://travis-ci.org/
* Go to your Profile page here: https://travis-ci.org/profile
* Activate the webhook for slf4j in the list of public repositories on the left
* Merge this pull request.

That's it! Travis will see the merge event and automatically build slf4j and run 'maven test' on it. From then on, any commit into qos-ch/slf4j will kick off a new build.

More details here: http://docs.travis-ci.com/user/getting-started/