Fix windows build

simplify test_security_curve.cpp with zmq_z85_encode

Added z85 codec to ZMQ API

* Removed redundant Z85 code and include files from project
* Simplified use of headers in test cases (now they all just use testutil.hpp)
* Export zmq_z85_encode() and zmq_z85_decode() in API
* Added man pages for these two functions

Fixed Z85 methods to be static

Support high water mark on inproc socket connect before bind.

Build didn't work if libsodium wasn't installed

Allow inproc sockets to connect before bind

Fixed overwrite in zmq_getsockopt

add exhaustive comparison in testutil bounce

On ZMQ_CURVE_xxxKEY fetches, would return 41 bytes into caller's 40-byte
buffer. Now these fetches only return 41 bytes if the caller explicitly
provides a 41-byte buffer (i.e. the option size is 41).

Fix preprocessor typoe

Minor fixes to project packaging

Fix Makefile.am for test_ctx_destroy

Implement non-blocking shutdown command

Fixed minor error in NULL mechanism (spec was wrong)

* This is passed to the ZAP handler in the 'domain' field

* If not set, or empty, then NULL security does not call the ZAP handler

* This resolves the phantom ZAP request syndrome seen with sockets where
  security was never intended (e.g. in test cases)

* This means if you install a ZAP handler, it will not get any requests
  for new connections until you take some explicit action, which can be
  setting a username/password for PLAIN, a key for CURVE, or the domain
  for NULL.