Problem: term "identity" is confusing

Solution: replace by "routing id"

src/router.hpp

@@ -85,7 +85,7 @@ namespace zmq
 
         //  If true, the receiver got the message part with
         //  the peer's identity.
-        bool identity_sent;
+        bool routing_id_sent;
 
         //  Holds the prefetched identity.
         msg_t prefetched_id;
@@ -123,7 +123,7 @@ namespace zmq
 
         //  Routing IDs are generated. It's a simple increment and wrap-over
         //  algorithm. This value is the next ID to use (if not used already).
-        uint32_t next_rid;
+        uint32_t next_integral_routing_id;
 
         // If true, report EAGAIN to the caller instead of silently dropping
         // the message targeting an unknown peer.