switch to WinXP toolset

Switched all projects to use "Visual Studio 2012 - Windows XP (v110_xp)"
toolset, as our stuff needs to run on Windows 2003 server
Added zmq.hpp to .gitignore

The header is part of the cppzmq project, copied here for ease of use
Change output directory structure for VS2012 projects

VS2012 property sheets do not provide for separate settings for different
configurations (Release, Debug, etc.). Now each configuration's output goes
in a separate folder so they can share names
Merge branch 'master' into local-master
Merge branch 'master' into local-master