Add figwheel nrepl middleware

[lvh]

Appropriate middleware might be:

["cider.nrepl/cider-middleware"
 "refactor-nrepl.middleware/wrap-refactor"
 "cemerick.piggieback/wrap-cljs-repl"]

Although it's not clear what happens when some of that's missing (e.g wrap-refactor). If we do this before #71 that will make #71 a bit easier since we won't have to document how to do (use 'figwheel-sidecar.repl-api) (figwheel-sidecar.repl-api/cljs-repl).

[lvh]

(We should also check if figwheel has actually started supporting this properly.)

[lvh]

This was closed in #72.