Merge pull request #38 from justinboswell/master

Fixed misaligned structure cast
Fixes backward compatibility with zmq 3.x

The code added in 'Fixed misaligned structure cast' implicitly assumes zmq 4.x, since it relies on new fields in zmq_event_t structure. This commit re-introduces the previous code if zmq < 4.x is detected.
Merge pull request #39 from zbierak/master

Fixes backward compatibility with zmq 3.x