feat: Pin and unpin Chats (#166)

* Added Pinning
- chat.pin() to pin
- chat.unpin() to unpin

Co-authored-by: Pedro S. Lopez <pedroslopez@me.com>

src/structures/Chat.js

@@ -57,6 +57,12 @@ class Chat extends Base {
          */
         this.archived = data.archive;
 
+        /**
+         * Indicates if the Chat is pinned
+         * @type {boolean}
+         */
+        this.pinned = !!data.pin;
+
         /**
          * Indicates if the chat is muted or not
          * @type {number}
@@ -124,6 +130,22 @@ class Chat extends Base {
         return this.client.unarchiveChat(this.id._serialized);
     }
 
+    /**
+     * Pins this chat
+     * @returns {Promise<boolean>} New pin state. Could be false if the max number of pinned chats was reached.
+     */
+    async pin() {
+        return this.client.pinChat(this.id._serialized);
+    }
+
+    /**
+     * Unpins this chat
+     * @returns {Promise<boolean>} New pin state
+     */
+    async unpin() {
+        return this.client.unpinChat(this.id._serialized);
+    }
+
     /**
      * Mutes this chat until a specified date
      * @param {Date} unmuteDate Date at which the Chat will be unmuted