feat: send typing in chat (#87)

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

src/structures/Chat.js

@@ -102,7 +102,17 @@ class Chat extends Base {
     async unarchive() {
         return this.client.unarchiveChat(this.id._serialized);
     }
+   
+    /**
+     * Start typing in chat. This will last for 25 seconds.
+     */
+    async sendTyping() {
+        return this.client.pupPage.evaluate(chatId => {
+            window.WWebJS.typing(chatId);
+            return true;
+        }, this.id._serialized);        
+    }
     
 }
 
-module.exports = Chat;
+module.exports = Chat;