add method to DanmakuTimer
add RingBuffer and BitmapRingBuffer
增加根据同屏弹幕数量动态控制字体anti alias
refactor RingBuffer and BitmapRingBuffer
调整绘制线程sleep时间
根据弹幕类型调整绘制顺序1
根据弹幕类型调整绘制顺序2
added DrawingCache class
增加一条碰撞检测规则
修复同屏滚动弹幕过多会超出屏幕的问题
update reamde