Add Travis CI build.

Hi!

I've added a Travis CI configuration that automatically builds and tests odds.
The tests already complete green for [my repository](https://travis-ci.org/nightscape/odds).
I've also added a badge which links to the build success of your repository and should become green once you have merged this PR and performed steps 1,2 and 4 from here:
http://about.travis-ci.org/docs/user/getting-started/

Using Travis CI greatly enhances transparency on the project's status and for me always is a good sign that I can start working on stuff and have a good set of tests that keeps me from doing stupid things :)

Best
  Martin