Time is now specified in minutes, not seconds fixes #8
mark the renamed method as private and give it a better prefix
Sometimes you really do get the strangest errors...

- removed the ability to use AfterDo on an instance, don't see
  the sense right now, and it would have made the new feature
  more complicated. Can be added back though if needed.
- As modifying classes is trickier, specs had to be restructured
spec for remove_all_calbacks
a bit of refactoring
simple support for an Array as the argument