add req-rep examples

req-rep/client.py

+import signal
+import zmq
+
+signal.signal(signal.SIGINT, signal.SIG_DFL)
+
+context = zmq.Context()
+
+#  Socket to talk to server
+print("Connecting to hello world server…")
+socket = context.socket(zmq.REQ)
+socket.connect("tcp://localhost:5555")
+
+#  Do 10 requests, waiting each time for a response
+for request in range(10):
+    print("Sending request %s …" % request)
+    socket.send(b"Hello")
+
+    #  Get the reply.
+    message = socket.recv()
+    print("Received reply %s [ %s ]" % (request, message))

req-rep/server.py

+import signal
+import time
+import zmq
+
+signal.signal(signal.SIGINT, signal.SIG_DFL)
+
+context = zmq.Context()
+socket = context.socket(zmq.REP)
+socket.bind("tcp://*:5555")
+
+while True:
+    #  Wait for next request from client
+    message = socket.recv()
+    print("Received request: %s" % message)
+
+    #  Do some 'work'
+    time.sleep(1)
+
+    #  Send reply back to client
+    socket.send(b"World")