Documentation incorrect  data-off-title should be  data-off-label

``` html
<input type="checkbox" data-off-title="No" data-on-title="Yes">
```

Also be nice if there was a way of controling the size via data attribute. At the moment I have to do this:

``` javascript
$this.checkboxpicker({
  defaultClass: 'btn-default btn-sm',
  offClass: 'btn-danger btn-sm',
  onClass: 'btn-info btn-sm'
}); 
```
