Added a jQuery plugin wrapper

This could be cleaner, but here is some code that now wraps the $.vegas plugin into a jQuery plugin.

It can now be used either in the current way (targeting the body element) or by specifying a target element e.g.:

    // Single image
    $("#myele").vegas({
        src:'img/background-1.jpg'
    })

    // Overlay
    $("#myele").vegas('overlay', {
        src:'img/overlays/13.png'
    });

    // Slideshow
    $('#myele').vegas('slideshow', {
        backgrounds:[
	    { src:'img/background-1.jpg', fade:1000 },
	    { src:'img/background-2.jpg', fade:1000 },
	    { src:'img/background-3.jpg', fade:1000 }
  	]
    }).vegas('overlay', {
        src:'img/overlays/11.png'
    });

    // Extra methods
    $('#myele').vegas('pause');

Not had much time to test, but all seems to be working!