code: function AtlasLoader(url, crossorigin) {
      EventTarget.call(this);
      this.url = url;
      this.baseUrl = url.replace(/[^\/]*$/, '');
      this.crossorigin = crossorigin;
      this.loaded = false;
  }
docs: The atlas file loader is used to load in Atlas data and parsing it
  When loaded this class will dispatch a 'loaded' event
  If load failed this class will dispatch a 'error' event
  @class AtlasLoader
  @extends EventTarget
  @constructor
  @param {String} url the url of the JSON file
  @param {Boolean} crossorigin