Speech speed control separate from master speed control

加入语速控制（独立于总倍速控制）以减少不必要的等待时间，用户可以在合理范围内自行设置。可额外考虑是否允许在用户设置的范围内上下随机抖动，以增加可游玩性。Speech Speed Control (seperate from master speed ctl) to reduce unessential waiting time. User can set in reasonable range. (May addtionally consider if allow a random vary near users' range set to make it more fun)