Clean up protocol doc-strings, minor housekeeping

This should be merge-able, but there's still some work that needs to be done:

TODO (me)
* I would like to rewrite the `ws-response`, `async-response`, `streaming-response` API for the new protocol API. I've got a few questions before I start with that.

TODO (you)
* Please rename the `close!` status `:unknow` to `:unknown`.
* Can you confirm: calling `(send! streaming-ch {:status _ :headers _ :body _} false)` will always work correctly? The :status and :headers will be stripped when it's not the first call, is that right? (The current protocol doc-string says so).

COMMENTS
* The current protocol doc-string also says that (send! websocket-ch {:status _ :headers _ :body _})` should work (:status and :headers will be stripped). I think that would be nice to have- if you agree, then you'll need to implement that in Java also.