Client-server pattern implementation (ZMQ_CLIENT)

[webmaxru]

The library is missing this important pattern described at https://rfc.zeromq.org/spec:41/CLISRV/

From the documentation: this pattern is meant to eventually deprecate the use of ZMQ_DEALER and ZMQ_ROUTER to build client-server architectures, as well as ZMQ_REP and ZMQ_REQ for request-reply.