In spite of there being considerable documentation sometimes in the
config file, we go with CC0 because we don't want the notion of
'derived work' of a config file.
The example `settings.conf` is also CC0. Add some docs to
it while we're at it.
- Use a named enum instead of a collection of booleans
- Support old-style configuration but complain about it
- Update AppImage config as well
The new setup allows four different restart modes: never,
always, user-unchecked and user-checked. The user-modes
are interactive and give the user a choice (defaulting to
unchecked-don't-restart and checked-do-restart respectively).
The non-interactive versions vary in how they are
displayed.
