Merge positioning branch to master

...ecify which portion of the photos to be shown.

2. Added "before" callback.
3. Renamed "eachcomplete" callback to "after".
4. Renamed "allcomplete" callback to "complete".
5. Simplified and fixed "percentOrPixel()" method.
6. Changed all "parseInt()" to "parseFloat()" to get more accurate values.
7. Replace 'px' from all atributes during plugin initialzation.