Fix documentation of beforeMove

The docs currently suggest that the current page index is passed as an argument, when in fact -- and more usefully for my application -- the next page index is the one passed in
Fix double-trigger of beforeMove

`beforeMove` was called in three places before:

1. at the start of `$.fn.transformPage`
2. in `$.fn.moveDown`
3. in `$.fn.moveUp`
4. in `$.fn.moveTo`

The last three all call `beforeMove` in order to actually move, which meant `befmoreMove` was always called twice. This commit take out the redundant calls, so it always comes from `$.fn.transformPage`.
Richer before/after move callbacks

Adds an extra parameter to the before and after public callbacks, passing in the next jquery element in addition to the index.

add functionality and update docs
Merge pull request #105 from uniphil/callbackEnhancement

Before/after move callback enhancements.