Support for Travis-ci (Continuous Integration Server)

Added support for the Travis-CI, a free continuous integration server (free for open-source projects) .

It's currently building the common.xml messages for Python, C, CS, WLua in Python 2.6, 2.7, 3.2 and 3.3. The result of the build of this exact commit is at https://travis-ci.org/DroidPlanner/mavlink/builds/32037313

To be useful the maintainer should enable the Travis-CI integration with the repo, which creates the web-hooks that tell Travis to start the builds.
This needs to be changed to point to ```https://travis-ci.org/mavlink/mavlink```

@LorenzMeier If you want to merge this PR I can make this modification