manual destruction of workers is currently needed

manual destruction is needed here i am afraid.
while i am trying to let the garbage collector do its work so it feels more like ruby
i have yet to find a way how to destroy the objects in the right order without
having to create a registry of sorts for czmq objects.
(you are supposed to terminate actors first which will then cleanup themself, but the way
at_exit works its the other way around ... and without the at_exit handlers
the process won't shut down with one SIGTERM or SIGINT, but only when you send them twice.)