Adds function to change slide

Adds a function to your jQuery element to change the slide. 

Example Markup:

```
<div class="slick-container">
  <div>your content</div>
  <div>your content</div>
  <div>your content</div>
</div>

```

Example JS:
```
var $slick = $('.slick-container').slick();
$slick.changeSlickSlide(2);
```

Re-minified using http://jscompress.com/