continuous integration using travis 

This pull requests adds continuous integration using travis, see https://travis-ci.org/thorbenk/Knossos for the working setup for my branch.

After merging

  - go to https://travis-ci.org 
  - sign in with GitHub, and enable travis for the `Knossos` repository 
    in your settings.
  - Change the build status image in `README.md` to point to the master branch of your own repository!