Small fixes to documentation

- REQ and REP sockets don't have HWM issues
- ZMQ_DONTWAIT applies to DEALER and PUSH only
Updated ZAP request for changed protocol draft

- username and password sent as two string frames
- fixed test case to match
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
Clarified man pages on mixed security
Introduced private constants for the context sanity tag values.
Ignored more MSVC intermmediate files.
Merge pull request #578 from gonzus/master

Changes to sanity tag in ctx
Merge pull request #577 from hintjens/master

API for CURVE configuration
Comments to clarify the socket name function
Merge pull request #579 from ianbarber/master

Clean up socket_type_string
Stop ZMTP handshake when an unexpected message comes
Merge pull request #580 from hurtonm/master

Stop ZMTP handshake when an unexpected message comes