favicon图标兼容

<link rel="apple-touch-icon" href="xxx>

<link rel="shortcut icon" type="image/x-icon" href="x">

<link rel="icon" type="image/x-icon" href="xxx>

<link rel="bookmark" type="image/x-icon" href="xxx>

<link rel="apple-touch-icon-precomposed" type="image/x-icon" href="xxx">