Travis-CI integratoin

This pull request adds Travis-CI integration to the repository. On each push to each branch, Travis-CI will automatically run tests. Pull requests will not display the status of the build, and the badge in the README will display the status of the build for master.

The hook for this repository is already enabled. The first build will start with the next commit to master. This integration has been tested using the repository at seliopou/ocaml-packet.