Merge pull request #572 from hintjens/master

Updated ZAP PLAIN request to follow latest draft
another iteration on ZMQ_PROBE_ROUTER
now it properly works for ROUTER
Merge pull request #573 from shripchenko/master

another iteration on ZMQ_PROBE_ROUTER
fix memory leak in tempnam() usage
Merge pull request #574 from pijyoi/master

fix memory leak in ipc_listener wildcard
added missing files required to build
Merge pull request #575 from murphybytes/master

Missing files in cmake generated build.
Implement ZMTP/3.0 CURVE handshake
Merge pull request #576 from hurtonm/zmtp_curve

Implement ZMTP/3.0 CURVE handshake
Added options for CURVE security

- ZMQ_CURVE_PUBLICKEY for clients and servers
- ZMQ_CURVE_SECRETKEY for clients
- ZMQ_CURVE_SERVERKEY for clients
- ZMQ_CURVE_SERVER for servers
- added tools/curve_keygen.c as example
- updated man pages