CalendarToday: Simplify with dates role changes.
DatesRole: simplify parse_datestring_to_date.

Since they guard their own inputs and return undef in case of failure,
we can just let them each try until we either get something or not.

Anchoring the guards makes sure we can tell descriptive from formatted.
00-roles.t: Update test output message.
DaysBetween: expand query-space like WorkdaysBetween.
DateMath: expand query-space with datestring_regex().