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: remove all remaining references to `zmq_utils.h`

I hope restoring this from a previous version doesn't do any damage, it
is missing in the current version of this repository and is vital for
the lib to compile anywhere.

Solution: remove this file

Solution: update to 2016

Solution: change zmq_poller_close(p) to zmq_poller_destroy(&p)

If we're going to add CLASS-like APIs we should use the proper
syntax; specifically 'destroy' instead of 'close', which is a
hangover from the 'ZeroMQ is like sockets' model we're slowly
moving away from.

Solution: change zmq_timers_close(p) to zmq_timers_destroy(&p)

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

We do not use 'get' for getters.

Solution: rename to zmq_msg_routing_id () for public API.

Solution: Move the macros to a private header.

Solution: Convert to spaces and remove trailing whitespace in these files.

Fixes not receiving unsubscription messages in XPUB socket with
ZMQ_XPUB_VERBOSE and using a XSUB-XPUB proxy in front.

This adds two modifications:

- It adds a new flag, ZMQ_XPUB_VERBOSE_UNSUBSCRIBE, to enable verbose
  unsubscription messages, necessary when using a XSUB/XPUB proxy.

- It adds a boolean switch to zmq::mtrie_t::rm () to control if the
  callback is invoked every time or only in the last removal. Necessary
  when a pipe is terminated and the verbose mode for unsubscriptions is
  enabled.

This commit adds ZMTP connection heartbeats described in
http://rfc.zeromq.org/spec:37/ZMTP.

Of course people still "can" distributed the sources under the
LGPLv3. However we provide COPYING.LESSER with additional grants.

Solution: specify these grants in the header of each source file.