update libzmq version checks for 4.0
more version check fixes
add Socket.monitor in CFFI backend
test monitor on PyPy
update 4.x constants
regen constant files
Merge pull request #420 from minrk/4.0

update libzmq version checks for 4.0

3.3 has been relabeled as 4.0 in preparation for starting the release cycle
update target zmq in setup.py
start changes for 14.0
Merge pull request #421 from minrk/changes14

start changes for 14.0
bundle libzmq-4.0.1
link libsodium if available in bundled libzmq
rename stopwatch to utils in cython backend

place to put everything from zmq_utils.h
expose zmq.curve_keypair

in Cython backend
add curve_keypair to cffi
curve_keypair docstrings
test curve_keypair
Merge pull request #424 from minrk/4.1

updates for zmq 4.0
don't import gc thread more than once

should close #425
Merge pull request #426 from minrk/gc

don't import gc thread more than once