Get some initial things working for headings and codeblocks, based off of headlines implementation

Author: MeanderingProgrammer

Diff for: .stylua.toml

@@ -0,0 +1,9 @@
+column_width = 120
+line_endings = 'Unix'
+indent_type = 'Spaces'
+indent_width = 4
+quote_style = 'AutoPreferSingle'
+call_parentheses = 'Always'
+
+[sort_requires]
+enabled = true

Diff for: README.md

@@ -1,2 +1,17 @@
 # markdown.nvim
+
 Plugin to improve viewing Markdown files in Neovim
+
+# Dependencies
+
+- [markdown](https://github.com/tree-sitter-grammars/tree-sitter-markdown/tree/split_parser)
+  parser for [treesitter](https://github.com/nvim-treesitter/nvim-treesitter/tree/master):
+  Used to parse `markdown` files
+
+
+# Related Projects
+
+- [headlines.nvim](https://github.com/lukas-reineke/headlines.nvim) - Same high level 
+  idea different features
+- [markdown-preview.nvim](https://github.com/iamcco/markdown-preview.nvim) - Uses browser
+- [vim-markdown-composer](https://github.com/euclio/vim-markdown-composer) - Uses browser

Diff for: lua/markdown/init.lua

@@ -0,0 +1,98 @@
+local state = require('markdown.state')
+
+local M = {}
+
+---@class UserHighlights
+---@field public heading? string
+---@field public code? string
+
+---@class UserConfig
+---@field public query? Query
+---@field public bullets? string[]
+---@field public highlights? Highlights
+
+---@param opts UserConfig|nil
+function M.setup(opts)
+    ---@type Config
+    local default_config = {
+        query = vim.treesitter.query.parse(
+            'markdown',
+            [[
+                (atx_heading [
+                    (atx_h1_marker)
+                    (atx_h2_marker)
+                    (atx_h3_marker)
+                    (atx_h4_marker)
+                    (atx_h5_marker)
+                    (atx_h6_marker)
+                ] @heading)
+
+                (fenced_code_block) @code
+            ]]
+        ),
+        bullets = { '◉', '○', '✸', '✿' },
+        highlights = {
+            heading = '@comment.hint',
+            code = 'ColorColumn',
+        },
+    }
+    state.config = vim.tbl_deep_extend('force', default_config, opts or {})
+
+    vim.api.nvim_create_autocmd({
+        'FileChangedShellPost',
+        'InsertLeave',
+        'Syntax',
+        'TextChanged',
+        'WinResized',
+    }, {
+        group = vim.api.nvim_create_augroup('Markdown', { clear = true }),
+        callback = function()
+            vim.schedule(M.refresh)
+        end,
+    })
+end
+
+M.namespace = vim.api.nvim_create_namespace('markdown.nvim')
+
+M.refresh = function()
+    if vim.bo.filetype ~= 'markdown' then
+        return
+    end
+
+    -- Remove existing highlights / virtual text
+    vim.api.nvim_buf_clear_namespace(0, M.namespace, 0, -1)
+
+    local parser = vim.treesitter.get_parser(0, 'markdown')
+    local root = parser:parse()[1]:root()
+
+    local highlights = state.config.highlights
+
+    ---@diagnostic disable-next-line: missing-parameter
+    for id, node in state.config.query:iter_captures(root, 0) do
+        local capture = state.config.query.captures[id]
+        local start_row, _, end_row, _ = node:range()
+
+        if capture == 'heading' then
+            local level = #vim.treesitter.get_node_text(node, 0)
+            local bullet = state.config.bullets[((level - 1) % #state.config.bullets) + 1]
+            vim.api.nvim_buf_set_extmark(0, M.namespace, start_row, 0, {
+                end_row = end_row + 1,
+                end_col = 0,
+                hl_group = highlights.heading,
+                -- This is done to exactly cover over the heading hashtags
+                virt_text = { { string.rep(' ', level - 1) .. bullet, highlights.heading } },
+                virt_text_pos = 'overlay',
+                hl_eol = true,
+            })
+        elseif capture == 'code' then
+            vim.api.nvim_buf_set_extmark(0, M.namespace, start_row, 0, {
+                end_row = end_row,
+                end_col = 0,
+                hl_group = highlights.code,
+                hl_eol = true,
+            })
+        end
+    end
+end
+
+return M

Diff for: lua/markdown/state.lua

@@ -0,0 +1,13 @@
+---@class Highlights
+---@field public heading string
+---@field public code string
+
+---@class Config
+---@field public query Query
+---@field public bullets string[]
+---@field public highlights Highlights
+
+---@class State
+---@field config Config
+local state = {}
+return state