markdown: remove the pandoc plugins

- Removes the pandoc plugins, as there is (only on my laptop), a
  conflict between the vim-pandoc* plugins and treesitter.
- Configure the folding feature for markdown files based on treesitter.
- Add in the configuration some markdown modules to be installed by
  treesitter.

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

after/ftplugin/markdown.lua

@@ -0,0 +1,7 @@
+-- Specific settings for markdown files
+--   Use treesitter for folding
+--   Disable the color column
+
+vim.opt.foldmethod="expr"
+vim.opt.foldexpr="nvim_treesitter#foldexpr()"
+vim.opt.foldlevel=0

init.lua

@@ -362,7 +362,7 @@ vim.keymap.set('n', '<leader>ss', require'telescope'.extensions.luasnip.luasnip
 -- See `:help nvim-treesitter`
 require('nvim-treesitter.configs').setup {
   -- Add languages to be installed here that you want installed for treesitter
-  ensure_installed = { 'c', 'cpp', 'go', 'lua', 'python', 'rust', 'tsx', 'typescript', 'vimdoc', 'vim', 'json' },
+  ensure_installed = { 'c', 'cpp', 'go', 'lua', 'markdown', 'markdown_inline', 'python', 'rust', 'tsx', 'typescript', 'vimdoc', 'vim', 'json' },
 
   -- Autoinstall languages that are not installed. Defaults to false (but you can change for yourself!)
   auto_install = false,