Vendor `refmttype`

[anmonteiro]

We're removing refmttype in reasonml/reason#2855, which was only made to support the uses in refmterr.

If there are still users/maintainers of refmterr, I'd recommend vendoring that code as part of reason-native / refmterr, since it can easily be written in userland.

[ManasJayanth]

Should it be a shipped as a separate tool (but maintained here in this repo) ? Even if the name resembles refmterr, I'm sure if the syntax conversion that refmttype provides, makes sense as a part of refmterr (I could be wrong!).

[ManasJayanth]

Apologies - compiler errors translated to Reason syntax does make sense inside refmterr. I confused it with reason-region-ocaml-reason translation functions reason-mode provides in Emacs.