Add explicit setup of expected namespaces

When connecting to an nrepl server, explicitly require clojure.pprint, and
use clojure.repl/doc.  When used with an nREPL server that didn't match
these assumptions, nrepl.el commands otherwise fail.
Merge branch 'feature/add-aux-requires' of https://github.com/hugoduncan/nrepl.el into hugoduncan-feature/add-aux-requires
Checkdoc fixes.
Merge branch 'hugoduncan-feature/add-aux-requires'