jQuery scrollTop and scrollLeft are notoriously slow, so still use them, but tray a faster means first

The company I work with (ResolverGRC.com) hosted this change.  We did extensive research into some resource issues we were having with various libraries.  It turns out, that waypoints was a pretty big contributor to the resource usage, and not because it was badly written, but because it uses jQuery's scrollLeft and scrollTop methods.  These methods are generally fast enough, but we found that with certain versions of Internet Explorer, these methods are indeed quite slow.  Enjoy, and thank you for the great plugin.