Proposal: expose the parser errors

[miniBill]

I would love to have access to the actual Parser.DeadEnds to show them more nicely with https://github.com/miniBill/elm-parser-error-extra.

One possibility is exposing the parser, but that also means exposing the AST, and documenting it.

A smaller change would be to have a different parse method that doesn't toString the DeadEnds.

I'm up for writing either PR, but would like to know what your preference is.

[MaybeJustJames]

Hi @miniBill thanks for this, great idea. I'd prefer not to expose internal implementation details, or to expose them as little as possible. Removing the (automatic) toString on the DeadEnds seems like a reasonable change to me. Can expose the deadEndToString function so that users can do that if they want to, or use your library.