[PHP-DOC] DIO Support on windows

[M. Sokolewicz]

As of PHP 5.0.0 Dio support (Direct I/O) is also available on windows, 
whereas it used to be available only on other systems. Now, the point of 
this is the following:
surely we should be removing the &note.no-windows.extension from the DIO 
main page. We should also replace it with something stating that support 
for windows wasn't added till PHP 5.

I've been looking at the current entities, and couln't find any which 
would point to such a thing. Keeping it as a normal string is not the 
correct approach IMHO, seen as I feel that it might be used more often.

Should I add the new entity and change it in the DIO docs? or just 
change the DIO docs and leave it there.