Solution: implement ZWS 2.0 which websocket transport for zeromq

Solution: update it

Free memory when curve_client sends invalid ready message.

Problem: Missing ZeroMQ_INCLUDE_DIR when only static lib is built

Problem: 4.3.2 is out, need new version

Solution: bump to 4.3.3

CVE-2019-13132

Solution: bump them

Solution: list new features and bug fixes

Solution: fix them

Solution: create buffers large enough to contain arbitrary metadata

Request handling leaked memory.  Depending on the application's use o…

Add relicense agreement from Lourens Naudé

Problem: no security policy

Solution: add SECURITY.md with supported branches and maintainers public keys for private communications

Problem: code doesn't follow libzmq naming conventions

Solution: rename types/variables that are inconsistent

Clarify documentation for zmq_unbind/disconnect and new batch options

Solution: restore separate zmq_unbind documentation, adding a note that the implementation
might be shared but the semantics are different and should not be mixed.
This avoids tying the API to the implementation details which might change for some
engines.

Solution: clearly advise users to avoid them in all cases to
avoid unforseen problems.
Also fix markdown syntax, applicable transport types and getter description.

Problem: variable and type names are not descriptive

Problem: {in,out}_batch_size must be configured at compiled time

Solution: use more descriptive names

This commit also improves comments related to some of the changes.

Solution: Added a socket option to configure them at runtime.

Problem: missing heartbeat test for draft sockets

Solution: Add heartbeat tests for CLIENT, SERVER, GATHER and SCATTER
    socket types. RADIO and DISH tests won't be added since heartbeating
    is not yet supported.

Problem: disconnect & unbind doc is misleading

* Problem: radix tree's apply function uses incorrect resizing logic

Solution: rewrite the function using a vector

The buffer is extended once by 256 bytes, which will not be enough if
the node holds data larger than this number.

Make it explicit that the two functions are identical.
Also document the expected disconnect behavior extensively
and illustrate the difference between disconnecting a
connected vs. bound endpoint.

CMake: don't try to link with librt on MinGW

On MinGW, librt will might will found as rt library in MSYS, but fails linking with "cannot find -lrt" error.
As librt is not avaiable on native Windows, we should never try to link with -lrt on MinGW (which is native Windows).

Add tests for SOCKS proxy support