Updated:
    src/metdata.hpp: Remove explicit "const" from key of std::map<>
       because the key is implicitly const already (see
       http://en.cppreference.com/w/cpp/container/map and
       http://www.cplusplus.com/reference/map/map/).

On some platforms (such as z/OS UNIX System Services) explicitly
declaring the map key as "const" causes template expansion errors
as it tries to create separate allocators for "const const std::string"
and "const std::string" only to find that they clash.  (Presumably
some compilers collapse these into one earlier.)

There are no template expansion errors if the map key is left to be
implicitly const.

Updated:
   builds/zos/README.md: Outlined process to transfer source from
     GitHub to z/OS UNIX System Services, including character set
     conversion for the source

z/OS UNIX System Services port: EAGAIN, SIGPIPE

Updated:
    src/signaler.cpp: Add close_wait_ms() static function to loop
       when receiving EAGAIN in response to close(), with ms long
       sleeps, up to a maximum limit (default 2000ms == 2 seconds);
       used in signaler_t::~signaler_t() destructor.

Updated:
   tests/testutil.hpp: Add signal(SIGPIPE, SIG_IGN) to
        setup_test_environment(), on z/OS (__MVS__)

Updated:
    README.md: Documented need for application to handle/ignore SIGPIPE

VS updates for socks, rem libsodium VS crypt32 dependency.

z/OS UNIX System Services port

Updated:
   README.md:  describes process of building/using DLL
   makelibzmq: Build DLL as well as static library (unless BUILD_DLL=false)
   maketests:  Dynamically link to ../src/libzmq.so if present
   runtests:   Explicitly place ../src at start of LIBPATH
   makeclean:  Also remove files created for DLL
   cxxall:     Bumped updated date to reflect last edit

builds/zos includes:
    README.md: Overview of z/OS UNIX System Services port (Markdown)
    makelibzmq: Compile src/*.cpp and make libzmq.a
    maketests:  Compile tests/*.cpp and make test_* executables
    runtests:   Run tests/test_* executables and report results
    makeclean:  Remove built files
    zc++: /bin/c++ wrapper supplying required build arguments
    cxxall: run zc++ for all *.cpp files in directory

    platform.hpp: pre-generated (and edited) src/platform.hpp for z/OS
    test_fork.cpp: updated tests/test_fork.cpp that completes on z/OS

Added test and doc section for ZMQ_SHARED message flag

Added ZMQ_SHARED message option to zmq_msg_get()

Add Docker support

Ensure EOL is present at end of utils file.

MacOS/Clang complain due to presence of -Wnewline-eof in CZMQ.

Code cleanup

Add test for unbinding inproc socket.

Resolve issue #949

Windows: if WSA error number is held, use directly.

It must be done this way, as WSAGetLastError returns 0 in these circumstances

vs2012: Add missing socks files

Don't delay reception of signal

- new code may help undersdtand issue #1108
  (https://github.com/zeromq/libzmq/issues/1108)
- code cleanups

Fix to build on OpenBSD