add options.element to forward a dom element to favico.js

Hey, I have the scenario, that I have several favicons in the head like this:
```
<link rel="icon" type="image/png" href="/favicon-192x192.png" sizes="192x192">
<link rel="icon" type="image/png" href="/favicon-160x160.png" sizes="160x160">
<link rel="icon" type="image/png" href="/favicon-96x96.png" sizes="96x96">
<link rel="icon" type="image/png" href="/favicon-16x16.png" sizes="16x16">
<link rel="icon" type="image/png" href="/favicon-32x32.png" sizes="32x32">
```
With a single instance of Favico.js only on the favicons was manipulated.
Using the "elementId" Option didn't worked too, because it overwrites the href with the empty src. This results then in a exception.

So I ended up with adding the option to pass a dom element directly to favico, which allowed me then to hack around the issue. This is the way how I use now favicon in my code.

```javascript
jQuery('head > link[rel="icon"]').each(function() {
	var newFavicon = new Favico({
		bgColor : '#c4662b',
		animation : 'popFade',
		element : this
		});

	faviconJS.push(newFavicon);
});


faviconJS.forEach(function(faviconJS) {
	faviconJS.badge(currentNotificationValue);
});
```

I was thinking about modifying favico, so the library itself can handle this multi icons in a proper way, but didn't wanted to make a so big change without knowing that there is interest.