Support printing to markdown

[shonfeder]

This would allow programmatic construction and transformation of markdown, and (in the special case of a no-op transformation) would serve as a markdown pretty printer.

Request by @jfrolich on at #230 (comment)

[cuihtlauac]

Not sure if it is already known. ocaml-lsp-server is stuck with 1.3.2:

(omd (and (>= 1.3.2) (< 2.0.0~alpha1)))

It's using Omd.to_markdown in doc_to_md.ml

I believe this is problematic.

[shonfeder]

@cuihtlauac Could you explain what kind of problems you're hitting on 1.3.2?

[cuihtlauac]

Because ocaml-lsp-server requires omd < 2 it is not possible to have it installed in the same opam switch as packages requiring omd >= 2. Being forced to choose between mutually exclusive dependencies is a problem, I believe.

[shonfeder]

Thanks for explaining. I think this issue is certainly top priority at the moment.

My suggestion for the moment would be to avoid depending on the pre-release versions of 2.0 for any production-grade projects. As noted in the README, we have not yet achieved feature parity with 1.3, and only just recently resolved the lingering bugs causing failures to satisfy the CommonMark spec.

[cuihtlauac]

You're right. Unfortunately, a number of projects have decided not to wait and are relying on 2.0 features, they probably had good reasons too.