Change Gemfile source to https
Update to latest celluloid version

Including changes from async_method! to async.async_method.
s/Private/Internal/ in TomDoc comments
Rework orphan cleanup

Because "reap orphans" is such a terrible and hilarious thing to put in code.
Oh, Unix, never stop.

* Change child pid list calculation to only pull the system process table once
* Reap children both after a failed shutdown of the master process and after a
  normal shutdown, since both cases can leave orphans
* Add test script for creating orphans
* Log orphaned processes as an error