Clj-Antlr with ANTLR alternative labels support

Fork of clj-antlr supporting ANTLRv4 alternative labels. At the moment it's just a rather bad patch to the library for my personal purposes, I may try to 'refactor' it and make a pull request later.

Version left as 0.2.5-SNAPSHOT

How to use

Original way is broken, you can now use it as following

(require [clj-antlr.coerce :as coerce]
         [clj-antlr.interpreted :as interpreted])
(defn parse
  [grammar-file input-file]
  (let [input-string (slurp input-file)
        grammar-str (slurp grammar-file)
        grammar (interpreted/grammar grammar-str)
        m (interpreted/parse grammar {} input-string)
        e (coerce/tree->sexpr m)]
    e))
(parse "grammars/Json.g4" "data/test.json")