Port tools.reader to Clojurescript

As part of the effort to get the Clojurescript compiler bootstrapped,
this is a patch porting org.clojure/tools.reader to clojurescript.

The port follows the Clojure implementation quite closely, except in the case of:

• Numbers: all numbers are reduced to js/Number
• Chars: reduced to string as in Clojurescript
• Macros: only used to compile in/out features (not) available in cljs builds
• There is no `(defn read [] ...)` zero arity implementation as we don't have `in`
• Custom implementation of clojure.lang.RT/nextID using an atom
• Run tests using: `lein cljsbuild test`

Contributors: Andrew Mcveigh, Jonathan Boston, Nicola Mometto and Thomas G. Kristensen