use foreach for ->visit

(performance hit is just a little too heavy elsewise)

	modified:   lib/List/Objects/WithUtils/Role/Array.pm
add bench/

	new file:   bench/array-constructors.pl
	new file:   bench/foreach_vs_visit.pl
add hash->maybe_set()

	modified:   lib/List/Objects/WithUtils/Role/Hash.pm
	modified:   lib/List/Objects/WithUtils/Role/Hash/Immutable.pm
	new file:   t/02_hash/maybe_set.t
Merge branch 'maybe-set'

* maybe-set:
  add hash->maybe_set()