Add Support for markdown.nvim

[avih7531]

I'd like to add support for the rending plugin markdown.nvim -- an awesome, real-time markdown generator for Neovim.

Happy to tackle this one later in the week, but by all means if somebody wants to beat me to it, here are the highlight groups.

Before I start, I would like feedback as to what elements should be which colors? As I'm not a maintainer (happy to become one) I don't provide this project creative direction, and therefore want to make sure that whatever I do truly sticks to @AlexvZyl and @5-pebbles vision. Would love some basic ideas on highlights and color groupings, but will probably make a few and send screenshots before I submit the pull request.

[5-pebbles]

We already have some basic markup support; I would link to those whenever you can (helps with consistency). You should use utils.blend with palette.bg for the heading background to work with different bgs.

The PR, which added markup support, was fairly recent, and so there are still some things we are figuring out. If you want to change something, you are welcome to try it; just make sure to reflect the changes in the base markup highlights.

[avih7531]

See #154

[AlexvZyl]

My apologies @5-pebbles and @avih7531. Running work, a startup and my wife's business takes a lot of my time. I think I will take you up on that maintainer offer, if you still want?

Here is my suggestion:
@avih7531 and @5-pebbles prepare releases (do work on dev without me) and then I just review releases when we merge into main. What do you think?

I will obviously still work when I find time. I just find myself to be unreliable.

[AlexvZyl]

So, basically:

Merging into dev requires one reviewer (you do not have to wait for me) but merging into main requires two reviewers.

I think this theme has a decent number of users so we do not want to break people's work machines. @5-pebbles Those extensive tests you are writing should protect us against that though!

[5-pebbles]

That sounds good to me