Merge pull request #48 from hintjens/master

Problem: segfault at zpipes_server_engine.h:521
Merge pull request #61 from hintjens/master

Basing off Zyre 1.0.0 stable
Merge pull request #64 from hintjens/master

Removed test step debugging
Merge pull request #65 from hintjens/master

Added yet more logging
Merge pull request #66 from hintjens/master

Implement process lockfile and run user/group
Merge pull request #72 from hintjens/master

Removed use of CZMQ_EXPORT in API
Unpin czmq from 2.2.0 on travis build

the zsock stuff just landed in czmq trunk, and we'll track trunk
until a new stable on czmq.
Merge pull request #73 from rpedde/update_travis

Unpin czmq from 2.2.0 on travis build
Broker drops PID after fork

Fixes #74

Also added a script, src/zbroker_daemon, to build and run zbroker as
daemon, using the zbroker_daemon.cfg config file.