Simplify VS project configs and harden MSBUILD script

Update cmake, mingw32 and msvc builds

This became necessary after b9c27481

This became necessary after 22d6a974

Batched VS builds, updated libsodium imports

Documentation for ZMQ_IDENTITY_FD sockopt

Update  cmake for split of plain_mechanism

Implement ZMQ_IDENTITY_FD sock option for linking socket identity to FD

Split plain_mechanism into client and server part

add untracked test_stream_timeout into .gitignore and tests/Makefile.am

Issue #1017: add ZMQ_HANDSHAKE_IVL time limit on connection handshake

curve: initialize crypto libs before usage

NULL: Implement ERROR handling

NULL mechanism sends ERROR command rather than READY command when ZAP
handler rejects the ZAP request (status code != "200"). The body of
ERROR command contains the status code as returned by ZAP handler.

Integrate GSSAPI option in VS UI options and props.

Update mechanism API so we can check for ERROR status