private void FavouriteWorker_DoWork(object sender, DoWorkEventArgs e)
        {
            // get message argument
            Status oldStatus = e.Argument as Status;

            // call twitter api
            TwitterClient client = new TwitterClient(_username, _password);

            try
            {
                Status newStatus = client.Favourite(oldStatus.Id);
                client.Close();

                // pass results to completed handler
                Status[] results = new Status[] { oldStatus, newStatus };
                e.Result = results;
            }
            finally
            {
                client.Abort();
            }
        }