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

lib/md013.js

@@ -28,6 +28,7 @@ module.exports = {
   "names": [ "MD013", "line-length" ],
   "description": "Line length",
   "tags": [ "line_length" ],
+  "parser": "markdownit",
   "function": function MD013(params, onError) {
     const lineLength = Number(params.config.line_length || 80);
     const headingLineLength =