wip plugins: configure environment for quarto

- Installs and configures the nvim-quarto plugin.
- Adds needed plugins and configuration from diving in the quarto
  kickstart configuration, which is damn huge.
- Adds the marksman parser for markdown, with its configuration.
- Adds the quarto filetype to the pandoc pluging.
- Loads the markdown snippets for the quarto filetype.
- Adds language support for treesitter.
- Installs and configure vim-slime plugin in order to execute emmbedded
  code (but it doesn't work as it misses a LOT of configuration).
- Documents very shortly the added plugins in the README.

Co-Authored-by: iGor milhit <igor@milhit.ch>

after/ftplugin/pandoc.lua

@@ -3,5 +3,7 @@
 --  See :h awa
 
 vim.opt.awa=true
--- vim.opt.foldlevel = 1
--- vim.opt.conceallevel = 2
+-- vim.opt.foldmethod = "expr"
+-- vim.opt.foldexpr = "nvim_treesitter#foldexpr()"
+vim.opt.foldlevel = 1
+vim.opt.conceallevel = 2

lua/plugins/markdown/markdownpreview.lua

@@ -2,15 +2,13 @@
 --  https://github.com/iamcco/markdown-preview.nvim
 --  https://github.com/iamcco/markdown-preview.nvim/issues/558#issuecomment-1514701537
 
--- Defines the filetypes that should be recognize by markdown-preview.
-vim.cmd([[ let g:mkdp_filetypes = ['markdown', 'pandoc',] ]])
-
 return {
   {
     "iamcco/markdown-preview.nvim",
     ft = {
       'pandoc',
       'markdown',
+      'pandoc.markdown'
     },
     lazy = true,
     build = "cd app && npm install && git reset --hard",

lua/plugins/markdown/mkdnflow.lua

@@ -17,7 +17,7 @@ return {
     ft = {
       'pandoc',
       'markdown',
-      'quarto'
+      'pandoc.markdown',
     },
     lazy = true,
     config = function ()

lua/plugins/markdown/pandoc.lua

@@ -1,18 +1,12 @@
 -- Install and configure Pandoc plugins: vim-pandoc, vim-pandoc-syntax
 
+-- Defines the filetypes that should be recognize by vim-pandoc. Allows
+--   mardown-preview to be available with pandoc filetype.
+vim.cmd([[ let g:mkdp_filetypes = ['markdown', 'pandoc', 'pandoc.markdown'] ]])
+
 -- Sets the pandoc formatting mode to hardwrap
 vim.cmd([[ let g:pandoc#formatting#mode="hA" ]])
 
--- Pandoc folding settings
---  Fold level 2 headings
-vim.cmd([[ let g:pandoc#folding#level=1 ]])
---  Enable YAML folding
-vim.cmd([[ let g:pandoc#folding#fold_yaml=1 ]])
---  Fold the entire frontmatter
-vim.cmd([[ let g:pandoc#folding#foldlevel_yaml=2 ]])
---  Fold fenced code blocks
-vim.cmd([[ let g:pandoc#folding#fold_fenced_codeblocks=1 ]])
-
 -- Keymaps to switch to soft or hardwarp, or to toggle.
 vim.keymap.set(
   'n',
@@ -45,8 +39,10 @@ return {
   {
     "vim-pandoc/vim-pandoc",
     ft = {
-		  'markdown',
-			'pandoc'
+		  "markdown",
+			"pandoc",
+			"pandoc.markdown",
+      "quarto",
 		},
     lazy = true,
   },
@@ -54,7 +50,8 @@ return {
     "vim-pandoc/vim-pandoc-syntax",
     ft = {
 		  'markdown',
-			'pandoc'
+			'pandoc',
+			'pandoc.markdown'
 		},
     lazy = true,
   },