Slides js 3

I added the next slide to the start callback, since you can't always infer it from the current slide and it's useful to have it if you want to build your own pagination and keep it in sink with the slider.

It would be nice if start and complete had the same signature, e.g.
start(current, next)
complete(current, next)
but that would break backward compatibility, so I didn't change the complete callback.

I compiled the coffee file, but I don't know what minifier you're using so I left the minified js file unchanged.