Get the self-reported Windows version number.
win.version is an auxiliary function for
A character string describing the version of Windows reported to be in use.
This function is only available on Microsoft Windows.
The result is based on the Windows
GetVersionEx API function,
which for recent versions of Windows reports the compatibility version,
and not necessarily the actual version (hence 8.1 and 10 may be reported
as 8). If the API call reports 8, this function returns