New option to animate items when they are removed

Hey Justin,

I added an option to smoothly fade/blind away items as they are removed from a Manifest input. For example:

```javascript
$('input#manifest').manifest({
    animateRemove: true
});
```

The option could also be used to pass down custom animation parameters:

```javascript
$('input#manifest').manifest({
    animateRemove: {
        duration: 500,
        easing: 'easeInOutQuint'
    }
});
```

I tried to be mindful of various possible styles for items, and that seemed to require an inner wrapper element during the removal/animation. Also, I did my best to avoid adding any dependencies (e.g. jQuery UI Blind animation, easing functions, etc).

Anyway, just a small little feature that has delighted some of my users, thought I'd share it.

Cheers,
Vlad