Add callback events for beforeSlide and afterSlide

[brandoniffert]

It would be nice if developers could supply a callback function for before and after slide.

[nicinabox]

There is currently an event after slide (slides.animated) that you can bind to.

$('body').on('slides.animated', function() {
  console.log('slide animated')
}

I could add an additional event before animation begins as well.

[brandoniffert]

Great. Missed that in the docs. Thanks for the plugin, love how simple it is.

[nicinabox]

Woohoo! :)