Add support for notes (#860)

* Add support for notes

* Ensure consistency with notes from ready payload

* Add getter method for users

* Minor tweaks

* Update warning messages

* More minor fixes

src/structures/ClientUser.js

@@ -36,6 +36,13 @@ class ClientUser extends User {
      * @type {Collection<string, User>}
      */
     this.blocked = new Collection();
+
+    /**
+     * A Collection of notes for the logged in user.
+     * <warn>This is only filled for user accounts, not bot accounts.</warn>
+     * @type {Collection<string, string>}
+     */
+    this.notes = new Collection();
   }
 
   edit(data) {