feat: tidy things up and implement more renderers

- Finished Library parser
- Fixed search continuations
- Improved channel parser
- Improved playlist parser
- Added support for posts of type poll
- Improved History parser
- Removed redundant code

lib/parser/contents/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;