add option to allow prevention of autoplay from reversing slide direction

A number of sites will typically advertise related or "up next" news items/galleries/etc. after the final slide, and that was the use case I was considering when writing this update. The only way I could think of to do this is currently is put a check in the onAfterChange callback to see if the user tried to advance past the last slide, and if so, display an interstitial of sorts. However, when in autoplay mode, this would never happen because the direction would reverse. I just wanted to add this option so that the carousel would attempt to advance past the last slide, and I could check for that condition and handle it however I wanted, also being able to pause it in that state as well.