Provide interface.

Also move iovec definition from implementation to interface.
Not clear to me at present if an incomplete type should
be used to avoid gratuitously including <sys/uio.h> in
the interface. The interface can't be used with this include.

include/zmq.h

@@ -215,6 +215,20 @@ ZMQ_EXPORT int zmq_recv (void *s, void *buf, size_t len, int flags);
 ZMQ_EXPORT int zmq_sendmsg (void *s, zmq_msg_t *msg, int flags);
 ZMQ_EXPORT int zmq_recvmsg (void *s, zmq_msg_t *msg, int flags);
 
+// XSI vector I/O
+#if ZMQ_HAVE_UIO
+#include <sys/uio.h>
+#else
+struct iovec 
+{
+    void *iov_base;
+    size_t iov_len;
+};
+#endif
+
+ZMQ_EXPORT int zmq_sendv (void *s, struct iovec *iov, size_t count, int flags);
+ZMQ_EXPORT int zmq_recvmmsg (void *s, struct iovec *iov, size_t *count, int flags);
+
 /******************************************************************************/
 /*  I/O multiplexing.                                                         */
 /******************************************************************************/

src/zmq.cpp

@@ -50,16 +50,6 @@
 #include <unistd.h>
 #endif
 
-// XSI vector I/O
-#if ZMQ_HAVE_UIO
-#include <sys/uio.h>
-#else
-struct iovec 
-{
-    void *iov_base;
-    size_t iov_len;
-};
-#endif
 
 #include <string.h>
 #include <errno.h>