Problem: needs a zeromq context for each mruby instance

[Asmod4n]

To properly shut down a process which has multiple mruby instances in it we have to assign a zeromq context to each mruby instance.
This is slow and makes use of the inproc:// transport impossible between mruby instances in a process.

If there would only be one zmq context for all mruby instances a interrupt to the zmq context would mean all mruby instances would loose access to zmq.