Test against last stable version of each minor version, including 4.0
Merge pull request #260 from kkoopa/zmq4

Test against last stable version of each minor version, including 4.0
Upgrading tests to use should.js v2.1.x
Merge pull request #262 from ryanlelek/master

Upgrading tests to use should.js v2.1.x
Merge branch 'master' of https://github.com/JustinTulloss/zeromq.node
Update NAN to 0.8.0