Problem: no documentation for zmq_poller_*

Solution: add initial documentation

doc/zmq.txt

@@ -142,7 +142,10 @@ Monitoring socket events::
 0MQ provides a mechanism for applications to multiplex input/output events over
 a set containing both 0MQ sockets and standard sockets. This mechanism mirrors
 the standard _poll()_ system call, and is described in detail in
-linkzmq:zmq_poll[3].
+linkzmq:zmq_poll[3]. This API is deprecated, however.
+
+There is a new DRAFT API with multiple zmq_poller_* function, which is described
+in linkzmq:zmq_poller[3].
 
 
 Transports

doc/zmq_setsockopt.txt

@@ -774,7 +774,7 @@ up.
 When ZMQ_ROUTER_MANDATORY is set to `1`, 'ZMQ_POLLOUT' events will be generated
 if one or more messages can be sent to at least one of the peers. If
 ZMQ_ROUTER_MANDATORY is set to `0`, the socket will generate a 'ZMQ_POLLOUT'
-event on every call to 'zmq_poll'.
+event on every call to 'zmq_poll' resp. 'zmq_poller_wait_all'.
 
 [horizontal]
 Option value type:: int