Propagate preventDefault() to original event, take 2

See #4 and #6. The purpose is to prevent **some** of the browser's default behavior (specifically the buggy `click` events) while still allowing scrolling, zooming, etc.

If `event.preventDefault()` and friends are called in the custom handler, they will be propagated to the original stop event. For API completeness, there's also an option `preventDefaultEnd` to control this behavior via event data.