Merge pull request #280 from kkoopa/master

Use MakeCallback
Use `zmq_msg_send` for ZMQ >= 4.0 -- see #269
Merge pull request #284 from kkoopa/4fix

Use `zmq_msg_send` for ZMQ >= 4.0 -- see #269
Exposes the Socket class as zmq.Socket
Merge pull request #287 from tcr/tcr-exposeconstructor

Exposes the Socket class as zmq.SocketConstructor
Works on new v8 and old
Updates
Fixed typo in history.md
Release
Updated NAN to 1.2.0
Merge pull request #310 from kkoopa/newv8test

Updated NAN to 1.2.0
fixed merge conflict