Add more nrepl middleware (feature request list)

[benjamin-asdf]

I don't know if there is already a list of potential next features somewhere.

1. step debugger would be sick
   -> does it seem feasable to take over cider.nrepl.middleware.debug https://github.com/clojure-emacs/cider-nrepl

-> maybe the implementation from lispy-clojure.clj https://github.com/abo-abo/lispy is an alternative.

2. eldoc for ns-unmap has a nil arglist (fix to show correct arglist)

3. complete local symbols (fn args and binding forms)

4. complete core.comment, maybe we only complete fns atm?