Fix jump to source, close #3

This fixes jump to source for jar files in clojure and clojurescript.
This also fixes jumping to src-paths in clj e.g. lighttable/nrepl/eval.clj.
I opted to unpack jarfiles to a consistent tempfile. I thought it would be helpful to cache created tempfiles to avoid unpacking each time and to allow dependencies to have temporary modifications

Following jumps should now work:
* clj - macros, clj core, dependencies, anything on src-paths
* cljs - cljs core, dependencies, anything on src-paths
  Note: cljs macros via :require-macros don't work because there's no metadata on them.

To QA this, `lein install` in lein-light-nrepl/. 

@ibdknox Could you give me permissions to release lein-light-nrepl on clojars? I believe you'd need to add me, cldwalker, to [the group page](https://clojars.org/groups/lein-light-nrepl).