Flag (ULONG) - input

Wait for a keystroke flag.

The possible values are:

• IO_WAIT
  Wait for an event if one is not available. The event returned is removed from queue.
  
• IO_NOWAIT
  Return immediately, with or without an event. If an event is returned, removed it from the queue.
  
• IO_PEEK
  Return immediately, with or without an event. Do not remove the event from the queue.
  
• IO_PEEKWAIT
  Wait for an event if one is not available. Return the event but do not remove it from the queue.