Added next section index to onLeave callback.
Updated readme.
Fix example.
Added next section index to onLeave callback.
Updated readme.
Fix example.
Merge branch 'add-next-index' of github.com:patrick91/fullPage.js into add-next-index

Conflicts:
	jquery.fullPage.js
Merge pull request #382 from patrick91/add-next-index

Added parameter `nextIndex` to onLeave callback #382, #375