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.
I'm on the fence about this. I was following the pattern set by `->Duration`, but aesthetically I think I prefer plain old `request` and `response` as the constructors.