Compatibility with Wasm_of_ocaml

[vouillon]

Wasm_of_ocaml uses a different representation for OCaml floats and JavaScript numbers, so we need explicit coercions (which are still optimized away by Js_of_ocaml).

Also, since JavaScript values get boxed, physical equality can no longer be used to test whether a value is undefined.
But as undefined == null, I have just simplified the test in option_of_js.

The WebAssembly implementation of the runtime functions caml_ojs_wrap_fun_arguments and caml_ojs_iterate_properties is provided by wasm_of_ocaml.

[mlasson]

Thanks for the PR ! wasm_of_ocaml looks super cool !

[OlivierNicole]

Hello, do you intend to make a new release with these changes? Js_of_ocaml will probably release a breaking change regarding float conversions soon-ish.

[OlivierNicole]

I see that it’s done, that was fast! Thanks a lot!