hierarchies emission working too.

renamed s/Object/Obj/ in the asdl definition to avoid clash with JS's builtin
Object.
Added more file header comments and a simple makefile to generate the AST.

Also adding the auto-generated cool_ast.js into the repo for now, so that users
don't really have to run Python 3.4 just to generate it.
added file-header comment to the autogenerated code too