根据手机屏幕的旋转，调整图片

function exchangeWindow(){
        if(window.orientation == 0)
        {
            $('#helpimg').attr("src","/images/road/help_0.jpg");
        }
        else{
            $('#helpimg').attr("src","/images/road/help_90.jpg");
        }
    }
    window.addEventListener("orientationchange",function(obj){
        exchangeWindow();
    });