Add basic support for zmq_socket_monitor

Signed-off-by: Ondrej Kupka <ondra.cap@gmail.com>
Add tests for zmq_socket_monitor

Signed-off-by: Ondrej Kupka <ondra.cap@gmail.com>
Make tests compatible with Go version < 1.1

Signed-off-by: Ondrej Kupka <ondra.cap@gmail.com>
Merge pull request #77 from tchap/zmq_socket_monitor

Add basic support for zmq_socket_monitor.