js_of_ocaml support

[zenhack]

It would be really nice to be able to use this in the browser. Right now this doesn't build with js_of_ocaml, because of at least the dependency on stdint, though I'm not sure if there's anything else?

If stdint is the only thing, then maybe this just reduces to https://github.com/andrenth/ocaml-stdint/issues/6, but I wanted to ask, lest I discover after putting in some work that it's a much bigger task.

(I'm also interested in getting the rpc layer working in the browser)