Idents again

Exports javascript reserved names without $ prefixes (using indexers instead) and fixes #179.

I'm not sure if you have a better idea for the fix though, as this way involves arbitrarily choosing a type for variables introduced in a lambda, which shouldn't matter as the types are never used, but still seems icky.

If this is ok I guess we can close #131 too, as exported names will never be mangled now.