public SimplerTimer CallPeriodically(int delayMillis, Action callback)
        {
            var timer = new SimplerTimer(0, delayMillis, callback);

            timer.Start();
            AddTimer(timer);
            return(timer);
        }
        public SimplerTimer CallDelayed(int delayMillis, Action callback)
        {
            var timer = new SimplerTimer(delayMillis, 0, callback);

            timer.Start();
            AddTimer(timer);
            return(timer);
        }