code: function(animator, target, duration, easing) {
                  this.callMixin();
                  this.target = target;
                  this.time = 0;
                  this.duration = duration;
                  this.easing = easing;
                  this.animator = animator;
                  this.beginValue = animator.beginValue;
                  this.finishValue = animator.finishValue;
                  this.setter = animator.setter;
                  this.status = "ready";
              }
docs: @constructor
  @for kity.Timeline
  @private
  @description 时间线应该由动画器进行构造，不应手动创建