getbool - ask user to type boolean value
int getbool (prompt,defalt);
Getbool is used to ask the user to type "yes" or "no". Prompt is a
string containing a message which will be printed; the user types
"yes", "y", etc., or "no", "n", etc. in response to the question.
Getbool returns 1 if "yes" (etc.) is typed, 0 for "no". If the
user types just a carriage return, then defalt is returned.
The user is informed if his response is not valid (e.g. "maybe"),
and the prompt-and-response cycle is repeated.
There is no provision for an "escape" answer (e.g. "I don’t