Add support for Finagle HTTP servers

This pull request adds preliminary support for Finagle HTTP. It provides constructors and Clojure-friendly wrappers for `Server`, `Request`, and `Response` objects, and basic `ServerBuilder` support. It does not yet attempt to wrap all possible getters and setters.
Thanks, glad you like it. I'm on the fence about overriding `get`, though. I dislike overriding core functions in ways that alter their arity or semantics, but I don't like the idea of naming it `oget` or `opt-get` (or something) either. Thoughts?