Problem: the new reimplementation of zmq_proxy_steerable had PAUSE/RESUME
that didn't follow expected behaviour. Possibly mixed up. Test didn't properly
cover the issue.
Solution: improve test coverage, fix the proxy command parsing.
I had no knowledge of the pre-MPL-2.0 implementation. This fix is based
on documented semantics and prior API usage. I contribute this
under MPL-2.0.
It is contriubted under the MPL-2.0.
I had no knowledge of the previous implementation of zmq_proxy_steerable().
This version was developed based on expectations set in the old man page with one exception. This version uses a REP/REQ for the proxy control protocol sockets. The old man page example used PUB/SUB which is nonsensical given the STATISTICS command requires two way communication.