code: function(isSmooth) {
                  var lc;
                  this.smooth = !!isSmooth;
                  if (this.smooth && (lc = this.lastControlPointSet)) {
                      this.updateAnother(lc, lc == this.forward ? this.backward : this.forward);
                  }
                  return this;
              }
docs: @method setSmooth()
  @for kity.BezierPoint
  @description 设置贝塞尔点是否光滑，光滑会约束顶点和两个控制点共线
  
  @param {Boolean} isSmooth 设置为 true 让贝塞尔点光滑