Feature request: handle extended markdown

[rjbou]

omd is used by opam2web, to generate opam.ocaml.org pages. Table rendering is now handled by omd as a plain text. It is one of the feature of the extended syntax.

I can share an image example if needed.

[nojb]

I agree that tables are useful to have. GFM-style tables are a suitable design, I think. Now all we need is an implementation.

[avsm]

This would be useful for RWO as well; we could do this as part of that effort once the RWO build migrates to omd master (cc @clecat )

[clecat]

It seems nice to do, I will see if I can do that as a secondary effect of my work on the migration

[XVilka]

To date, most of the Markdown parsers and producers support at least some of the extensions, so having them indeed is very useful.

[nojb]

We are planning to have them. But for the initial release of version 2 (which we are working to have out the door as soon as possible), we are going to focus on having strict commonmark compatibility. Extensions will come after that. Thanks!

[nojb]

Moved this one to #205