Scrollwheel Support

[jgwhite]

Scrollwheel events should trigger prev/next behaviour on microfiche under cursor.

$('#my-slideshow').microfiche({ scrollwheel: true });

We don’t want microfiche capturing scrollwheel events like embedded Google Maps do.

Though with Mac trackpads we could arguably bind up the full touch controls, I think we should aim for a more general implementation—simply prev/next—for this release.