Added CSS3 transforms support for better mobile performance

CSS3 GPU animations
-------------------

Using CSS3 `translate3d` significantly improves animation performance, especially on mobile devices, you can force CSS3 translations with this new option.  

<pre>
	csstransforms3d
</pre>
If set to true, it means that css3 3D transforms (on the GPU) are available and should be used for all animations over the slower `jquery.animate`. 
Default: false

Should be set to the value of a feature detect (e.g. using Modernizr)

<pre>
$('#container').freetile({
	...
	selector: '.grid-item',
	csstransforms3d: $('html').is('.csstransforms3d')
});
</pre>

*Gotcha: CSS transforms do not effect document flow so your tile container height will no longer reflect the true height of your grid* 

Make sure you are also using CSS3 transitions on each element in your grid to get it to animate: 

<pre>

.grid-item{
	webkit-transition: all .25s ease-out;
	-moz-transition: all .25s ease-out;
	-o-transition: all .25s ease-out;
	-ms-transition: all .25s ease-out;
	transition: all .25s ease-out;
}

</pre>