Fix multiple slide issue #6

* added `”use strict”`
* code optimization
* callback `onLoadingComplete` now returns 2 new arguments: all images
object (JSON) and plugin element (DOM)
* callback `onSlideComplete` now returns 4 new arguments: current slide
index (Number), current image element (DOM), all images object (JSON),
and plugin element (DOM)
Fix Wikipedia link markdown error, update callbacks doc, fix Jquery → jQuery