Add support for PersistentQueue

I took a little liberty with the interface in order to keep the JS API consistent, but I can change it if it does not match your vision.

There is a small issue regarding printing a PersistentQueueSeq (e.g., by executing `mori.rest(mori.queue(1,2,3))` due to a [minor defect](http://dev.clojure.org/jira/browse/CLJS-800) in ClojureScript.  The current behavior is to print a not-so-friendly view of the data structure (instead of causing a 'Maximum call stack size exceeded' error and crashing node).  As soon as that ticket is resolved, I will create another pull request here or add to this one to make PersistentQueueSeq inspectable.