markdown updates

[tpeacock19]

Hello, I was using this package recently, trying to get it to work
with treesit-fold and ended up making some other improvements.

I added more settings for treesit to enable thing navigation and
outline integration. Figured I would create a PR if you are
interested.

[LionyxML]

Hello there @tpeacock19!

I am very happy you found it useful and spent some time improving it, thanks! :)

Sorry it took me so long to answer your PR. Life really got in the way this time, but now I'm trying to get some side projects moving and dedicate some time to it.

Would you mind explaining why drop the 'imenu' and besides the awesome treesit-fold support, how to test the outline integration? (I mean, I am kind of missing M-x imenu, but it wasn't properly working though).

Also, I have a 'version' of this project I am trying to patch within Emacs it self. Would like to colaborate on this? Are you familiar with the FSF copyright assignment? (https://www.fsf.org/bulletin/2022/fall/copyright-assignment-with-the-fsf)