This is a part of #2717
Some settings didn't get getters because
- They are transient parse settings (e.g. ignore errors)
- They get propagated to args and should be checked there
`is_allow_hyphen_values_set` is a curious case. In some cases, we only
check the app and not an arg. This seems suspicious.
When an Arg uses .min_values(0), that arg's value(s) are effectively
optional. This is conventionaly denoted in help messages by wrapping the
arg's values in square brackets. For example:
--foo[=value]
--bar [value]
This kind of argument can be seen in the wild in many git commands; e.g.
git-status(1).
Signed-off-by: Peter Grayson <pete@jpgrayson.net>
