Add support for :if/:then/:else and :cond statements

Now we can do conditionals in a monadic context (we ported the code from algo.monads to this project)

Also we upgraded libraries:
- lein-cljsbuild to 0.3.2
- lein-dalap to 0.1.1
- buster-cljs to 0.1.2
- clojure to 1.5.1