Added pauseAutoPlay/resumeAutoPlay methods to control slideshow, fix #25
Delay property now uses milliseconds internally
Added documentation for pauseAutoPlay/resumeAutoPlay methods
Added tests for autoPlay on pauseAutoPlay method
Added support to visibilitychange events, fixes #23
Fixed problem with resuming autoPlay time, had to switch slideshow interval to use setTimeout instead
Added some useful comments
Added support to Page visibility API as a feature on README file
Added constructor to doc file