Prep repository for running tests on Travis-CI

This adds the .travis.yml configured to run the test suite against ruby
1.9.3, 2.0, and 2.1. It also adds a link to the build status badge to
the repo's README (references the non-existent path for tmm1/pygments.rb).
Now we just need to have the repo authorized by one of the maintainers.
Might want to add `?branch=master` to this :)