Compiler improvement

Do no merge, Review only.
* example:
   * rm warning
* compiler
  * parsing (javacript)
     * javascript parser from facebook/pfff ( successfully parsed jquery)
     * more coming .. 
  * refactoring
  * cleanup
     * Primitive.mark_used
  * short variable names
     * delay var assignment
     * compute js variables liveness
     * use ocamlgraph to color the graph of js variables (Js_var.ml) (disabled by default)
  * fix
     * remove `ouput_file` in case of compilation failure
     * profile 3 (`-opt 3`) : missing deadcode elimination btw inline and flow
  * static evaluation of constant
  * improve parallel renaming by tracking deps.
  * sharing
      * javascript string
      * alias primitives
  * static evalution
  * detect caml_format_int "%d"