Travis

Fixes #29. Travis provides excellent integration with github. It will chime-in as necessary for pull-requests.

I've been working on pull-req stuff for bitcoin core, and figured this would be a good test-case to see how viable  Travis is.

See an example build-matrix here. https://travis-ci.org/theuni/secp256k1/builds/27738000

To take the pull-req features for a test-run before pulling, you can submit a pull req to my travis branch here: https://github.com/theuni/secp256k1 

To setup: head to https://travis-ci.org and give it the necessary api access to your repo. After that, any branch that contains a .travis.yml file will be built for each push/pull-req.