Fix bug on IE6

Hi, I have test this script running on IE6, there only 2 issue
1. 'use strict' not support, you need disable it with IE
2. In end of Hash, do not add comma
Add unselect public method

Example:

```javascript
$(el).selectonic("unselect", $(el).find("li:even")
```
Merge remote-tracking branch 'origin/patch-2'