Just housekeeping.

Thanks for the gem!

I added an MIT License.  Some people assume public domain when no license is stated, but legal departments at large companies have a problem with software that doesn't explicitly state a license, so it is important to state.

If you want a different one, just change the text of `LICENSE`, and the `gemspec`.

I also made the gem's version accessible from Ruby, by making it a constant in the Rusen namespace: `Rusen::VERSION`.  This is the current best practice, and makes the gem compatible with other gem tools, like `gem-release`.

I also setup specs to run against Ruby 1.8.7, 1.9.2, 1.9.3, 2.0.0, and jruby 1.9.