Amazingly, we have camlp4+pa_js working!

Based on ocaml-with-pp project.  It parses to Parsetree.structure
rather than Parsetree.toplevel_phrase which means no directives.
Apart from #install_printer we're not missing much at the moment.

Also brought back runtime.js to fix a very odd printf problem where
it was going to console.log when called in a lwt context with
xmlHttpRequest.  This solution properly overrides the js_print_*
functions.  Will look at this again.