Add kibit Clojure linter plugin

Issue #230.
Apply recommendations from kibit

This applies the recommendations made by kibit to the project. Common
patterns include using (when x y) instead of (if x y nil), and using the
inc and dec functions instead of (+ x 1) and (- x 1).

Issue #230.
Add a Clojure linter script

This adds a scripts/linter directory which contains a script to execute
the clojure linter. In the future, different linters will each have an
script here.
Merge branch 'issue/230'