Support Windows platform

See issue https://github.com/zeromq/aziomq/issues/7

Implementation notes:
1. boost::asio::ip::tcp::socket class used to wrap ZMQ_FD type.
2. std::thread replaced with boost::thread because the first one can not be used during static variables initialization/deinitialization
3. Library build as static instead of share, because it is more common for C++ libraries on Windows.
4. Static version of Boost libraries are searched by default.
5. Release or debug version of ZeroMQ is used depending on configuration.
6. No ZeroMQ version checking implemented
7. Either static or dynamic version of ZeroMQ can be used. It's controlled by ZMQ_STATIC variable, which is 0 by default.
This is an inadvertent leak, what really needs to happen is sd_->release() (e.g. tell the stream descriptor to release the FD, not leak the stream_descriptor*), otherwise the asio reactor will attempt to close the zmq FD.