TADS 3 Library: banner manager

This module defines the banner manager, which provides high-level services to create and manipulate banner windows.

A "banner" is an independent window shown within the interpreter's main application display frame (which might be the entire screen on a character-mode terminal, or could be a window in a GUI system). The game can control the creation and destruction of banner windows, and can control their placement and size.

This implementation is based in part on Steve Breslin's banner manager, used by permission.