usablica/intro.js — pull request #127 by drgomesp (2013-05-12 13:51:01+00:00)
Title: Before change callback

This PR allows the developer to bind custom callbacks to be called before the change event occurs.

```javascript
var introJs = introJs();

introJs.onbeforechange(function() {
console.log('This is fired BEFORE the change occurs');
});

introJs.onchange(function() {
console.log('This is fired AFTER the change occurs');
});

introJs.start();
```