Treesitter based Syntax Highlighter for MyST (support neovim)

[mmcky]

It would be nice to have syntax highlighting for MyST in neovim based on the treesitter parser.

There are currently two markdown parsers available including

1. treesitter-grammars for markdown
2. tree-sitter-markdown which is a third party developed extension

It would be nice to extend these to include MyST features such as roles and directives.

Notes

Syntax highlighting for directives is somewhat complex due to not knowing what is contained within the directive. It could be code or markdown or rST for example. We could assume MyST for now and parse the inside of each directive as such or build a supported catalog of directives.