Melange compatibility

[jchavarri]

@aantron would you support making this library compatible with Melange? I don't think many changes would be needed, mostly a couple of changes on opam and dune files. cc @davesnx

Using Melange would unlock a fix for #52.

[jchavarri]

One thing that comes to mind is that because melange also uses dune, a new library should be added, maybe they could be called promise.native and promise.melange or something like that.

[davesnx]

I have vendored this project under server-reason-react on https://github.com/ml-in-barcelona/server-reason-react/tree/main/packages/promise, and changes that I made was:

• Add dune file for js/
• Remove type Result and result dependency on native/ (was there for compatibility with 4.02)
• Remove type result on js/ (was there for compatibility with BuckleScript < 6)

Just my 2 cents about ReScript/Melnage. If there's a need for a compatibility with ReScript (#73) maybe we could migrate either js/promise.re to ReScript and keep it under a bsconfig folder or migrate to OCaml and add the dune with the modes melange.

I have done this similar stuff for styled-ppx and it's a decent solution