Initial markdown support

Markdown doesnt have a language server, so do this manually
Closes #43

lua/symbols-outline.lua

@@ -5,6 +5,7 @@ local ui = require('symbols-outline.ui')
 local writer = require('symbols-outline.writer')
 local config = require('symbols-outline.config')
 local utils = require('symbols-outline.utils.lsp_utils')
+local markdown = require('symbols-outline.markdown')
 
 local M = {}
 
@@ -58,12 +59,14 @@ end
 
 function M._refresh()
     if M.state.outline_buf ~= nil then
-        vim.lsp.buf_request_all(0, "textDocument/documentSymbol", getParams(),
-                                function(response)
+        local function refresh_handler(response)
             if response == nil or type(response) ~= 'table' then
                 return
             end
-            if not utils.is_buf_attached_to_lsp(vim.api.nvim_get_current_buf()) then
+
+            local current_buf = vim.api.nvim_get_current_buf()
+            if (not utils.is_buf_markdown(current_buf)) and
+                (not utils.is_buf_attached_to_lsp(current_buf)) then
                 return
             end
 
@@ -75,7 +78,13 @@ function M._refresh()
 
             writer.parse_and_write(M.state.outline_buf,
                                    M.state.flattened_outline_items)
-        end)
+        end
+
+        if vim.api.nvim_buf_get_option(0, 'ft') == 'markdown' then
+            refresh_handler(markdown.handle_markdown())
+        end
+        vim.lsp.buf_request_all(0, "textDocument/documentSymbol", getParams(),
+                                refresh_handler)
     end
 end
 
@@ -96,7 +105,10 @@ function M._highlight_current_item(winnr)
 
     local doesnt_have_outline_buf = not M.state.outline_buf
 
-    local should_exit = doesnt_have_lsp or doesnt_have_outline_buf or
+    local is_not_markdown = not utils.is_buf_markdown(0)
+
+    local should_exit = (doesnt_have_lsp and is_not_markdown) or
+                            doesnt_have_outline_buf or
                             is_current_buffer_the_outline
 
     -- Make a special case if we have a window number
@@ -250,15 +262,17 @@ end
 
 function M.toggle_outline()
     if M.state.outline_buf == nil then
-        vim.lsp.buf_request_all(0, "textDocument/documentSymbol", getParams(),
-                                handler)
+        M.open_outline()
     else
-        vim.api.nvim_win_close(M.state.outline_win, true)
+        M.close_outline()
     end
 end
 
 function M.open_outline()
     if M.state.outline_buf == nil then
+        if vim.api.nvim_buf_get_option(0, 'ft') == 'markdown' then
+            handler(markdown.handle_markdown())
+        end
         vim.lsp.buf_request_all(0, "textDocument/documentSymbol", getParams(),
                                 handler)
     end