Solution: fix them

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

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

Solution: add space between OR'ed values

zmq_getsockopt.3 2472: warning [p 17, 9.5i, div '3tbd1,1', 0.5i]: can't break line
zmq_setsockopt.3 3471: warning [p 24, 1.8i, div '3tbd1,1', 0.5i]: can't break line

Solution: mark test_rebind_ipc as XFAIL on Hurd as it does not
implement getsockname on IPC and thus it's impossible to use
wildcard IPC binds.
Document that ZMQ_LAST_ENDPOINT does not work on Hurd with IPC.

* Add ZMQ_ROUTER_NOTIFY draft socket option

Solution: add a new ZMQ_MULTICAST_LOOP option for UDP sockets.

Solution: revert the revert!

Revert "Problem: regression in 4.2.3 went unnoticed, want to release 4.2.5"

This reverts commit 5f17e26f.

Solution: revert DRAFT -> STABLE API transition so that we can do a
bugfix-only 4.2.5 release.
Will be re-reverted once tagged.

Revert "Problem: ZMQ_BINDTODEVICE has met STABLE conditions"

This reverts commit 3cb79f50.

Revert "Problem: ZMQ_MSG_GSSAPI_* have met STABLE conditions"

This reverts commit 374da420.

Revert "Problem: ZMQ_MSG_T_SIZE has met STABLE conditions"

This reverts commit 6411c4a2.

Revert "Problem: docs say STABLE API still in DRAFT"

This reverts commit 9f2f30b7.

Solution: update them

Solution: add ZMQ_ZAP_ENFORCE_DOMAIN to hide backward incompatible
change and make it disabled by default.
In a future release that breaks API compatibility we can then switch
the default to enabled in order to achieve full RFC compatibility.

Fixes #2762

Solution: Replaced by "routing id"

Solution: change docs to refer to "Routing id"

Solution: fix documentation

Solution: Replaced by "routing id"

Solution: change docs to refer to "Routing id"

Linux now supports Virtual Routing and Forwarding (VRF) as per:

https://www.kernel.org/doc/Documentation/networking/vrf.txt

In order for an application to bind or connect to a socket with an
address in a VRF, they need to first bind the socket to the VRF device:

    setsockopt(sd, SOL_SOCKET, SO_BINDTODEVICE, dev, strlen(dev)+1);

Note "dev" is the VRF device, eg. VRF "blue", rather than an interface
enslaved to the VRF.

Add a new socket option, ZMQ_BINDTODEVICE, to bind a socket to a device.
In general, if a socket is bound to a device, eg. an interface, only
packets received from that particular device are processed by the socket.

If device is a VRF device, then subsequent binds/connects to that socket
use addresses in the VRF routing table.

Problem: GSSAPI NAMETYPE options were not documented in man
pages for zmq_getsockopt() and zmq_setsockopt().

Solution: add new options to these manual pages.

Solution: add paragraphs to zmq_get/setsockopt man pages

The effect can be seen on http://api.zeromq.org/4-2:zmq-getsockopt at
options ZMQ_USE_FD and ZMQ_RATE.

Solution: fix length of squiggly line under option title

These options are confusing and redundant. Their names suggest
they apply to the tcp:// transport, yet they are used for all
stream protocols. The methods zmq::set_tcp_receive_buffer and
zmq::set_tcp_send_buffer don't use these values at all, they use
ZMQ_SNDBUF and ZMQ_RCVBUF.

Solution: merge these new options into ZMQ_SNDBUF and ZMQ_RCVBUF.

This means defaulting these two options to 8192, and removing the
new options. We now have ZMQ_SNDBUF and ZMQ_RCVBUF being used both
for TCP socket control, and for input/output buffering.

Note: the default for SNDBUF and RCVBUF are otherwise 4096.

The proper name is ZMQ_THREAD_SAFE

Solution: fix in the documentation.

Solution: rename to ZMQ_MAXRT

This is the option name used on Windows, so easier to use and
remember.

Solution: rename socket option (and variables and files) from usefd
to use_fd.

Solution: rename socket option (and variables and files) from
pre_allocated_fd to usefd.

Solution: add new [set|get]sockopt ZMQ_PRE_ALLOCATED_FD to allow
users to let ZMQ use a pre-allocated file descriptor instead of
allocating a new one. Update [set|get]sockopt documentation and
test accordingly.

The main use case for this feature is a socket-activated systemd
service. For more information about this feature see:
http://0pointer.de/blog/projects/socket-activation.html

Solution: Replace with `zmq_ctx_term`

VMCI transport allows fast communication between the Host
and a virtual machine, between virtual machines on the same host,
and within a virtual machine (like IPC).

It requires VMware to be installed on the host and Guest Additions
to be installed on a guest.

Fixes #1646

Solution: fix documentation

Solution: change option behaviour and adopt documentation

- both are thread safe
- they do not accept ZMQ_SNDMORE nor ZMQ_RCVMORE

Solution: add man pages/sections for:

 * ZMQ_SERVER
 * ZMQ_CLIENT
 * ZMQ_THREADSAFE
 * zmq_msg_routing_id
 * zmq_msg_set_routing_id