With this function you can get the internal Windows id value
(the HWND, a pointer). This function is really only useful
for extension writers who need the window handle to call
Windows API's in DLL code (the returned pointer should be cast into
a string and then in the C++ just cast it to an HWND).
NOTE: This functions is for Windows and Mac OSX only (on Mac OSX it contains a pointer to an NSWindow class).
win_id = windows_handle();
The above code will store the game window id in a variable.