Windows support for FFI #1394
Description
In #1376 we held off on Windows support for FFI due to issues with packaging libffi on Windows detailed in #1090 (comment). But now that we have static linking of libffi on all platforms with libffi-0.2, Windows support should just be a matter of using the appropriate functions from the Win32 package to dynamically load shared libraries. We also need to figure out how to make the FFI tests work on Windows as well.