play = function play() {
                    _this3.playing = setTimeout(function () {
                        removeClass(list[index], CLASS_IN);
                        index += 1;
                        index = index < total ? index : 0;
                        addClass(list[index], CLASS_IN);
                        play();
                    }, options.interval);
                }
Play the images
@param {boolean} [fullscreen=false] - Indicate if request fullscreen or not.
@returns {Viewer} this