Small updates

* Added some small changes to the README.
* Renamed the Rakefile from (lowercase) rakefile.
* Added the Travis CI integration build. For it to be useful, you'll have to enable it. Follow [this link](http://www.smashingmagazine.com/2014/04/08/how-to-build-a-ruby-gem-with-bundler-test-driven-development-travis-ci-and-coveralls-oh-my/#a11) on how to do it.