10.7.1. Exercise [45 min]

Modify the RaceHorse class to get the previous standings from a DBM hash (keyed by the horse's name) when the horse is created, and update the standings when the horse is destroyed. For example, running this program four times:

my $runner = RaceHorse->named("Billy Boy");
$runner->won;
print $runner->name, " has standings ", $runner->standings, ".\n";

should show four additional wins. Make sure that a RaceHorse still does everything a normal Horse does otherwise.

For simplicity, use four space-separated integers for the value in the DBM hash.