Menu entries are often also available in toolbars or other widgets. And
sometimes, we want to enable or disable a given action, and this means
having to update everywhere this action is allowed.

This module helps managing actions in a the Tk manpage GUI: just create a
new object, associate some widgets and bindings with 'add_widget()' and
then de/activate the whole action at once with 'enable()' or 'disable()'.