title: CreateJS get the total frame number of a spritesheet
body: <p>I am building a spritesheetbuilder class when I can pass in spritesheets that may have a different number of total frames and I would like to know is there a way to dynamically find out how many frames there are in a spritesheet and then loop through them all without having to setup the animations frame by frame? The loop parameter is a boolean value already working. </p>
  
  <pre><code> //SpriteSheetAnimator(bmp, w, h, loop)
   this.monitor = new SpriteSheetAnimator(loader.getResult('img'), 204, 189, true);
  
   //inside the SpriteSheetAnimator object
    this._ss = new createjs.SpriteSheet({
                      animations:{
                          play:{
                              frames: [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22],
                              speed: 0.4
                          },
                      images:[this.bmp],
                      frames: {
                          width:this.width,
                          height:this.height,
                          regX:this.width*0.5,
                          regY:this.height*0.5
                      }
                  });
  </code></pre>