ZMQ_ROUTER_NOTIFY doesn't have a context and doesn't play nice with protocols. with ZMQ_DISCONNECT_MSG we can set it to a protocol message, like DISCONNECT in majordomo. Router will send it when a peer is disconnected. Another advantage of ZMQ_DISCONNECT_MSG is that it also works on inproc.

Together with ZMQ_HEARTBEAT it allows to build very reliable protocols, and much simpler as well.

problem: ZMQ_HEARTBEAT is not useful without sending an hello message

When using ZMQ_HEARTBEAT one still needs to implement application-level heartbeat in order to know when to send a hello message.
For example, with the majordomo protocol, the worker needs to send a READY message when connecting to a broker. If the connection to the broker drops, and the heartbeat recognizes it the worker won't know about it and won't send the READY msg.
To solve that, the majordomo worker still has to implement heartbeat. With this new option, whenever the connection drops and reconnects the hello message will be sent, greatly simplify the majordomo protocol, as now READY and HEARTBEAT can be handled by zeromq.

* Allow CMAKE to generate ws and wss transports
I guess there is little use of just ws transport, so by default
GnuTLS (and libsodium) are enabled

* cmake libzmq including wss transport (ubuntu 19.10 and ubuntu 19.10 + wsl 1.0)
test_security_fails (libsodium assert !?)

* updated relicense

* make external libs gnutls nss sodium optional

* #ifdef WSS classes and functions, build test*ws* only if correct libs are included, warning if libs not present

* make libsodium optional

* cmake fix tests TIPC transport

* clang-format pointed out a wrongly placed #ifdef

* GnuTLS before 3.6.7 is not safe

* msvc doesn't agree with strlen in array declaration, test_socks now at least compiles on windows

* windows: libsodium build fails, missing include dirs set by env var

* ws transport test only works when GnuTLS is found

* Fixed condition to use NSS / built in SHA1, so that test_ws_transport should now pass, also when GnuTLS is not found

Problem: poller sleeps forever if no events

Problem: poller item fd uninitialized

Solution: Fail with error if no events are active and timeout is infinite

Solution: Set to zero for socket events

* Problem: boilerplate when init msg from data copy

Solution: Add zmq_msg_init_buffer to construct
a message by copying memory from buffer.

Problem: Strange zmq_poller doc formatting

Solution: Add newlines and extra asterisks

Problem: zmq_send doc does not match declaration

Solution: add const to pointer type

Problem: ZMQ_THREAD_SAFE is not bool

Solution: Change documentation value type to int

Fix gitignore tracking file list

Solution: Fix .gitignore's exceptions for sources in tools/

Install CMake config to LIBDIR by default, to correctly support multiarch

Signed-off-by: FeRD (Frank Dana) <ferdnyc@gmail.com>

Solution: Install CMake config in arch-dependent LIBDIR/cmake

Using "share/cmake/${PROJECT_NAME}" as DESTINATION for installing
ZeroMQConfig.cmake et al works for arch-independent configs, but
is wrong for multiarch. The configs for each version of the
library should be stored below the arch-dependent LIBDIR, using
the GNUInstallDirs ${CMAKE_INSTALL_LIBDIR} variable.
Signed-off-by: FeRD (Frank Dana) <ferdnyc@gmail.com>

Refactor protocol literals into constants

Some ifdefs in condition checking may cause problem in some compiler or
static analyzers. When PGM and NORM both are disabled, some condition
will be derived as false || false.

Solution: Splitted condition checking for every ifdef conditions

Conditinoal compile for OPENPGM and NORM is mixed.
Also found few codes which needs conditional compile but not applied.

Solution: Apply conditional compile preprocessors

Solution: replace into named constants

Optimizing gitignore files

Solution: optimize gitigore using patterns
 *  Categorize ignoring lists
 *  Use pattern to remove similar lists
 *  Marked source files to be tracked

Problem: msg_t functions do not respect coding style

Solution: fix them

Add UDP transport to related docs

* UDP is mentioned as available transport, and it also supports
  wildcard addresses, but not mentioned
* zmq_unbind(7) also mentions about wild-card endpoint in zmq_bind(3)

Solution: add udp in wildcard address related docs

zmq_bind(3) and zmq_connect(3) does not mention UDP as available
transport types.

Solution: add udp mentioning line for related docs

Problem: building on OS X may failed

Solution: Add troubleshooting guidelines to resolve

(Relicensing statement added)

* ip_resolver_t: adding virtual descructor to silence C++-warning -Wnon-virtual-dtor

* adding my relicense

News out of date, formatting not clean

Solution: run make clang-format-diff