Build & pass request map, not just URI

I needed cookie/session data when handling my websockets, so I'm building a request map using ring-servlet and adding to map sent over connection-chan rather than just URI. Allows access to basic set of request data, including headers, query params, [etc](https://github.com/ring-clojure/ring/blob/0cf09cc9a57e8a4422cdaa5783e62b7890a745d4/ring-servlet/src/ring/util/servlet.clj#L34-49). Not sure if you're interested in this, @lynaghk, since it changes the interface slightly, but others might find this helpful. I'll update the tests if you are interested