Support for wikilinks in gfm/commonmark

[AndreiPashkin]

Currently, using version 3.1.8 I'm having a hard time converting a Markdown document with wikilinks to a Markdown document without wikilinks using gfm input format. But at the same time it works if I replace gfm with markdown.

Example source file:

# Test

![[Attachments/test.png]]

And the Pandoc command is like this: pandoc -f gfm+wikilinks_title_after_pipe -t gfm --resource-path='<my-attachments-path' --columns=120 -o out.md in.md

And the result is:

# Test

\![Attachments/test.png](Attachments/test.png "wikilink")

Related to #8853.

[jgm]

Clarification: wikilinks work fine with gfm, but the wikilinks extensions for gfm/commonmark don't support putting a ! in front of a wikilink to make it an image.