Static Library Linking for Windows

- New ZMQ_STATIC flag to enable "libzmq.lib" Windows static library (or "libzmq_d.lib" in Debug mode).
- ZMQ_STATIC needs also to be defined by projects using static linking against "libzmq.lib"
- New StaticDebug & StaticRelease configurations for libzmq Win32 projects under MSVC 2008 & 2010
- Tested with Visual Studio 2008 Express under Windows 7, and Visual Studio 2010 Express under Windows 8.