Add Rule.parser property for custom rules to specify which Markdown parser output they use, honor it strictly, and add full type support.

lib/md024.js

@@ -10,6 +10,7 @@ module.exports = {
   "names": [ "MD024", "no-duplicate-heading" ],
   "description": "Multiple headings with the same content",
   "tags": [ "headings" ],
+  "parser": "markdownit",
   "function": function MD024(params, onError) {
     const siblingsOnly = !!params.config.siblings_only || false;
     const knownContents = [ null, [] ];