code: function(callback) {
  		if (this.instance) {
  			this.instance.createPage(function(page) {
  				callback(page);
  			});
  		} else {
  			var that = this;
  			this._createInstance(function() {
  				that.createPage(callback);
  			});
  		}
  	}
docs: Creates a PhantomJS page, to be called with a callback, which
  will receive the page.
  
  @param  {!function(?)} callback Function to be called after the
  page is created, it receives the page object.
  @public