Controls screen updating.
onoff|| (optional) specifies action to take with pending updates.
- True --- (not zero) All pending updates are performed. In addition
a flag is set for the current window indicating that all future
updates to that window should be performed immediately.
- False --- (zero) no screen updates are performed until either
refresh() or refresh(true) is called, or
an input call is made.
- Not specified --- All pending updates are performed.
Opens several windows with only one screen update: