Solution: update to 2016

Tests were failing, because some deque calls were causing undefined
behavior: calling front() or pop_front() on an empty deque. Such
calls are now safeguarded.

The patch fixes the issue #1568.

The patch fixes lingering subscriptions that occur upon disconnection
on XPUB sockets with option XPUB_MANUAL when used in a XPUB-XSUB
proxies.

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

Fixes tests that were introduced in a previous pull request. See
https://github.com/zeromq/libzmq/pull/1539#issuecomment-132968987

This patch  adds a new member of type deque to the
xpub class that contains pointers to metadata_t.
This deque is then used (alongside pending_data
and pending_flags) to preserve metadata when
copying messages.

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.

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.

ZMQ_INVERT_MATCHING reverses the PUB/SUB prefix matching. The subscription
list becomes a rejection list. The PUB socket sends messages to all
connected (X)SUB sockets that do not have any matching subscription.

Whenever the option is used on a PUB/XPUB socket, any connecting SUB
sockets must also set it or they will reject everything the publisher
sends them. XSUB sockets are unaffected because they do not filter out
incoming messages.

Solution: update for 2015

Fixes #1320

It's bad practice to start by testing all exceptional conditions
and then dropping through to the 'normal' condition. Apart from
being inefficient, it's deceptive to the user. Conditional code
should always try to show the natural expectation of the code,
with exceptional cases coming last.

Solution: clean up this code.

- not initialized before use
- name is nasty (boolean variables should not have negative names)

Solution: rename to 'lossy' and initialize to 'true'.

icanhasall is cute (for now), but the effect of the variable is clear
only after tracking down its origin reading the commit. This change is
intended to make it easier for people to have some intuition about its
effect from its name.

Copyrights had become ads for Sustrik's corporate sponsors, going against the original
agreement to share copyrights with the community (that agreement was: one line stating
iMatix copyright + one reference to AUTHORS file). The proliferation of corporate ads
is also unfair to the many individual authors. I've removed ALL corporate title from
the source files so the copyright statements can now be centralized in AUTHORS and
source files can be properly updated on an annual basis.

Fixed 7 MSVC2008 Compiler Warning (level 3) C4800: 'const int' : forcing value to bool 'true' or 'false' (performance warning)

- added explicit test "(xxx != 0)" to get a "bool" value out of the "int" expression
- see the MSDN recommandation http://msdn.microsoft.com/en-us/library/b6801kcy(v=vs.90).aspx

zmq::xpub_t::xread_activated() – change to process messages without 0
or 1 prefix, but without affecting subscriptions

zmq::xsub_t::xsend() – change to send rather than discard messages
without 0 or 1 prefix, but without affecting subscriptions

Update documentation

XPUB "verbose" mode excludes unsubscriptions

Compiling without warnings is a good goal, because it makes
new warnings (which probably indicate bugs) stand out rather
than getting lost in the spam.

My fixes fall into two categories:

    - Adding (void) casts of unused parameters, where their
      unusedness seems like a TODO (or in some cases a bug?).

    - Removing parameter names altogether, where the function
      is clearly a stub that will never use its parameters.

Should be no change in behavior.

* Implemented new ctx API (_new, _destroy, _get, _set)
* Removed 'typesafe' macros from zmq.h
* Added support for MAX_SOCKETS (was tied into change for #337)
* Created new man pages