Adds Array.flat in both capacities refs #2632
Adds Array.flat in both capacities refs #2632

perl6/doc,perl6/doc,MasterDuke17/doc,MasterDuke17/doc,MasterDuke17/doc,MasterDuke17/doc,tbrowder/doc,perl6/doc,tbrowder/doc,perl6/doc,tbrowder/doc,tbrowder/doc,perl6/doc