Update ZMQ
Update ZMQ

$ git shortlog v4.0.7..055de7f --no-merges
Dylan Cali (5):
      add test_proxy_single_socket to gitignore
      add tests for zeromq/libzmq#949
      backport zeromq/libzmq@54e0fde
      backport zeromq/libzmq@09e7416
      Updated NEWS

Jean-Christophe Fillion-Robin (6):
      README: Add hyperlinks to explicitly reference reposistories
      FindAsciiDoc: fix CMP0053 warning with cmake 3.1
      place a ZMQ_UNUSED macro and replace all unused variables with ZMQ_UNUSED macro
      rename ZMQ_UNUSED macro to LIBZMQ_UNUSED
      Problem: Private/internal macros defined in public header.     Solution: Move the macros to a private header.
      Fix unused parameter and variable warnings.

Josh Blum (2):
      Fix static library name overlap under MSVC
      Fix C linkage for public symbols MSVC

Luca Boccassi (6):
      Solution: check for libtoolize in autogen. Fixes #131
      Do not use ldconfig in CI if running on OSX
      Add OSX build to travis config. Fixes #133
      Increase file limit in travis config
      Problem: CI may fail due to timeout. Fixes #135
      Enable container-based build

Min RK (1):
      backport stream socket empty frame fix

Pieter Hintjens (1):
      Updated version to 4.0.8 for next release

leonarf (1):
      THREAD PRIORITY option documentation

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