Type information in Rescript syntax in Docs

[Lomand]

Rescript part of the Docs should have examples and type definitions displayed in Rescript syntax (Right now both are displayed in Ocaml).

Example: 'a -> 'b -> 'c -> 'a * 'b * 'c -> ('a, 'b, 'c) => ('a, 'b, 'c)
People with no experience in Ocaml will find the first version confusing and cryptic.

Since currently there is no way to use Rescript parser programmatically (melange-re/melange#228) the only option is to convert interfaces from .mli to .resi, and read the type information from them. Sound suboptimal, but works surprisingly well (488/499 types converted without a hitch). There were some problems (rescript-lang/syntax#449) with Tablecloth.Map.String and Tablecloth.Set.String type definition (type nonrec 'value t = 'value Of(TableclothString).t), I had to rewrite the type to equivalent

  type identity

  type nonrec 'value t = (TableclothString.t, 'value, identity) t

Since you are in process of refactoring the current implementation (#229) this will no longer be an issue when this PR merges.

There is a need for some testing just to check if everything is alright and also fix broken type definitions in submodules.

I also want to convert all examples in rescript docs to rescript syntax, I'll address this in another PR.

[Lomand]

The PR is ready. The only type that failed to generate is Internal.toBeltComparator. It's not exposed externally in the library, so this issue can be ignored (this type is not displayed in the docs). Other than that, everything is looking normal.

[pbiggar]

great, thanks! I looked at it over the weekend, will try to get it merged today.

[pbiggar]

This is great, thank you!