pause() {
    if (!this.paused && this.playing) {
      remove(this);
      this.paused = true;
      this._pauseTime = KEC.Time();
      if (this._onPause !== undefined) {
        this._onPause.call(this);
      }
    }
    return this;
  }
Pause tweening
@returns {Tween} this instance