refactor!: finish parser migration

Finally! :)

This removes all code related to the old parser.

#65

lib/parser/classes/Post.js

@@ -0,0 +1,13 @@
+'use strict';
+
+const BackstagePost = require('./BackstagePost');
+
+class Post extends BackstagePost {
+  type = 'Post';
+
+  constructor(data) {
+    super(data);
+  }
+}
+
+module.exports = Post;