New (major) version released (not compatible with previous one).

Version 2.0.0 ready. Changes:
 - Methods to remove pages added.
 - Feature to change class names used added.
 - Feature to add button elements linked to each page to indicate the
   current one added.
 - Custom callbacks and method to enable, disable and set them added.
 - Feature to change CSS property used to trigger callbacks (after
   transitionEnd event) added.
 - Minor code improvements.
 - Feature to add loading class to pages added.
 - Improved comments on the code.
 - Improved Readme (but still a lot to do here).