added elapsedForHumans method, along with new supporting constants

elapsedForHumans adds the ability to print out time elapsed in a human readable format (i.e. "2 years, 3 weeks, 1 day, 10 hours, 5 minutes, 3 seconds ) I purposely left out whether it's time remaining or time that has past for my own needs, but you could easilly add that back in if necessary. Anyway I saw it was requested, wanted it for myself as well, so here it is.