Merge pull request #63 from pblasucci/master

Improved diagnostics API and did some general code clean-up
When setoption RCVTIMEO is set on the socket, recv may return null (Option.None). adds check for this situation
When setoption RCVTIMEO is set on the socket, recv may return null (Option.None). adds check for this situation
Merge pull request #68 from hammett/recv_fix

Recv fix
added more zguide examples
cancelLinger may fail, and if it does, the socket wont be closed, leaving the context_term hanging.
Merge pull request #69 from hammett/master

cancelLinger may fail, and if it does, the socket wont be closed, leavin...
Merge branch 'master' of https://github.com/zeromq/fszmq
Many small changes:
- Fixed release date in notes for v4.0.6
- Updated  Version unit test to 4.0.6
- Fixed bug in vs_netmq throughput test
- Reverted unnecessary changes to Socket finalization process
- Reverted inappropriate change to Socket.recv method
- Added another zguide example (mtrelay)