Merge pull request #34 from rodgert/master

Pull detail::specialized_socket out of versioned namespace
Enable advanced CTest features to better integration with CI
Merge pull request #35 from oliora/master

Enable advanced CTest features to better integration with CI
Check that version of ZeroMQ found matches the requested one (all platforms).
Merge pull request #36 from oliora/master

Check that version of ZeroMQ found matches the requested one
Merge remote-tracking branch 'upstream/master'