A native node addon for obtaining system idle time in seconds.

OS implementations derived from the following resources:

• http://www.danandcheryl.com/2010/06/how-to-check-the-system-idle-time-using-cocoa
• https://github.com/jojobyte/idlerun
• https://github.com/rosedu/Pidgin/blob/master/pidgin/gtkidle.c