Add once and as_array "filters" to Mojolicious

diff

diff --git a/lib/Mojolicious/Validator/Validation.pm b/lib/Mojolicious/Validator/Validation.pm
index b46d63552..d702daa62 100644
--- a/lib/Mojolicious/Validator/Validation.pm
+++ b/lib/Mojolicious/Validator/Validation.pm
@@ -68,11 +68,16 @@ sub optional {
 
   return $self->topic($name) unless defined(my $input = $self->input->{$name});
 
+  my %filters = map { ($_ => 1) } @filters;
+  my ($wantarray, $wantscalar)
+    = (delete $filters{as_array}, delete $filters{once});
+
   my @input = ref $input eq 'ARRAY' ? @$input : ($input);
-  for my $cb (map { $self->validator->filters->{$_} } @filters) {
+  for my $cb (map { $self->validator->filters->{$_} } keys %filters) {
     @input = map { $self->$cb($name, $_) } @input;
   }
-  $self->output->{$name} = ref $input eq 'ARRAY' ? \@input : $input[0]
+  $self->output->{$name}
+    = ref $input eq 'ARRAY' && !$wantscalar || $wantarray ? \@input : $input[-1]
     if @input && !grep { !length } @input;
 
   return $self->topic($name);