Need a header file that undefs all defines in windows.h
===

To be tidy, I want to `#undef` everything defined in `windows.h`.

E.G:

    namespace os_stuff
    {
        #include <windows.h>

        // ARGH! Macros everywhere!

        // at least I can keep the rest of the API in here
    }

    // include a bunch of files here that use the Windows API through os_stuff

    namespace os_stuff
    {
        #include <unwindows.h> // <- #undefs all that was #defined in windows.h
    }

    // All clean, as though windows.h was never here. Though os_stuff, used nowhere else,
    // still has all of the API declarations in it (which is OK).