preliminary travis-ci integration

This is a skeleton of travis-ci integration. See https://travis-ci.org/ghorn/LibClang

TODO:
- use @chetant account instead of @ghorn on the README build status thingy
- add a .travis.yml file to all branches even if they are not being tested, see http://about.travis-ci.org/docs/user/build-configuration/#Specify-branches-to-build