Obsidian reader extensions for comments and wikilink transclusions

[kepano]

Add Obsidian-Flavored Markdown #9883 using Markdown extensions. I could use some guidance on the approach to transclusion, and what to do on the writer side.

Extensions

• comments: Parses %%text%% as comments (removed from output)
• wikilink_transclusions: Parses ![[Title]] for full file transclusion
• wikilink_heading_transclusions: Parses ![[Title#Heading]] for heading transclusions
• wikilink_block_transclusions: Parses ![[Title#^id]] for block transclusions
• block_ids: Parses ^id at paragraph end, wraps paragraph in Div with that ID

Uses insertIncludedFile for transclusion.

Includes tests and manual updates.

[jgm]

Transclusion should be possible. See insertIncludedFile from Text.Pandoc.Parsing.
And look at the RST reader's treatment of include directives for an example of its use.

[kepano]

@jgm I think this is in a good place for your review now.

Some notes:

1. I revised how wikilink images (e.g. ![[image.jpg]]) are parsed because the implementation of Image wikilinks for export in Obsidian #8853 via 09de84f seemed to be originally driven by Obsidian's syntax. In Obsidian, the ![[link]] wikilink syntax can be used to transclude any type of file (not just images), as well as headings and blocks within Markdown files. I consolidated all of these into a new transclusion parser (which could alternatively be called "include" or "embed" if you prefer).
2. I ended up building on top of the Markdown reader instead of the Commonmark reader. Hopefully this gives flexibility to other apps that support Obsidian's syntax but not other Commonmark extensions.

[jgm]

Can you rebase this into one commit, or a few logically coherent commits? All API changes should be clearly described and marked as such [API change] in the commit messages, so we won't miss them in the changelog.

[kepano]

Can you rebase this into one commit, or a few logically coherent commits? All API changes should be clearly described and marked as such [API change] in the commit messages, so we won't miss them in the changelog.

Done!