Initial markdown support

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

lua/symbols-outline/markdown.lua

@@ -0,0 +1,37 @@
+local M = {}
+
+---Parses markdown files and returns a table of SymbolInformation[] which is
+-- used by the plugin to show the outline.
+-- We do this because markdown does not have a LSP.
+-- Note that the headings won't have any heirarchy (as of now).
+---@return table
+function M.handle_markdown()
+    local lines = vim.api.nvim_buf_get_lines(0, 0, -1, false)
+    local results = {}
+
+    for line, value in ipairs(lines) do
+        if string.find(value, "^#+") then
+            if #results > 0 then
+               results[#results].selectionRange["end"].line = line - 1
+               results[#results].range["end"].line = line - 1
+            end
+
+            table.insert(results, {
+                kind = 13,
+                name = value,
+                selectionRange = {
+                    start = {character = 1, line = line - 1},
+                    ["end"] = {character = 1, line = line - 1}
+                },
+                range = {
+                    start = {character = 1, line = line - 1},
+                    ["end"] = {character = 1, line = line - 1}
+                }
+            })
+        end
+    end
+
+    return {[1000000]={result=results}}
+end
+
+return M