Reerror: error-resilient parsing (same as Merlin for OCaml)

[let-def]

This PR implements a new "parsing loop" that is more robust to errors and should improve the experience in an IDE.

The parser itself is not affected (we still have a declarative grammar), but we now have a slightly different interpretation in interactive use-cases.

[let-def]

Esy is missing the "fix" dependency. I don't know the proper way to update it.

[ulrikstrid]

I can add @opam/fix via a resolution in a package.json. I wonder if this is a bug with parsing the .opam file in esy.

cc @andreypopp

[jordwalke]

Been testing this out and it's so good.
@ulrikstrid - it wouldn't be a resolution, it would just be a regular dependency.

@let-def you just add "@opam/fix": "*" to the "dependencies" section of src/refmt/esy.json and ./esy.json (the later is just the development-time package configuration, the later is what will be released).

If you just add those fields, the CI should pass and we can release this puppy.

[jordwalke]

Did you want to delete this file?

[let-def]

Yes

[jordwalke]

Woohoo! Closing now that it's merged (after @anmonteiro rebased it). Very excited to announce this one.