create a finagle adapter

[sprsquish]

I created an adapter for Twitter's Finagle RPC system. I'm new to clojure and I used this as a learning experience so some of the code may be a little rough.

I'd love to hear any feedback though!

[weavejester]

Thanks for the patch, but we're not adding any more adapters to the main Ring repository.

However, this would be great if released as its own project.