Adding Travis support

Travis (http://travis-ci.org/) provides free integration testing hooked
into GitHub. Writing this config file (.travis.yml) is the most
difficult part in setting it up. There are only three steps left:

 1. Sign into Travis with your GitHub account
 2. Activate GitHub webhook for this project
 3. Merge this pull request

Only one test will fail unless pull request #136 got merged.
Merge pull request #137 from mkllnk/travis-support

Adding Travis support