Added directional swiping events.

I needed to have a swipe up and swipe down gesture on a view.  On the callback block I couldn't figure out how to detect up or down.

So, I thought I'd attach two different gesture events and use the direction option.   RMQ wouldn't let me attach to swipes.  

Now it can.

I didn't write any tests because I'm not convinced you'll actually like this because it introduces a possible conflict between :swipe and :swipe_up.  Not sure how'd you'd like to address this.

No offense will be taken if you'd like to burn this PR to the ground.