Explore using stil4m/elm-syntax instead of elm-ast

[dillonkearns]

Using https://github.com/stil4m/elm-syntax may potentially address a few problems:

• The elm-ast libraries have several parsing bugs
• The elm-ast libraries are not planning on upgrading to Elm 0.19
• Using elm-syntax may also help with only parsing modules which are imported somewhere

Here's the original comment suggesting this library: #15 (comment)

Here are some current issues in elm-typescript-interop it could address:

• Performance for large projects Performance for large projects #16
• Ignore unimported modules Ignore unimported modules #11
• Parsing bugs like Parsing error on - sign or -- sign #15 and several others

[davetapley]

If #18 is merged, then FYI it will have to be updated if we move away from elm-ast.

[muelli]

I'm throwing in a wild idea:
How about some manual pre-processing of the modules?
In particular, stripping -- comments to alleviate the problems experienced in #15.

Also note https://github.com/andre-dietrich/parser-combinators

[dillonkearns]

I suggested the manual preprocessing in a github issue a while back for the Bogdanp parsing library, but it seems like that one isn't being actively maintained lately (at least the last I checked).

I think the still4m package is the way to go. It will take some time to change things over, though and I don't have much bandwidth at the moment, but I'll go that route when I do it.