Make Map.pick()/roll() about 7x faster
Make Map.pick()/roll() about 7x faster

- on a 26 element Hash, larger hashes faster still
- doesn't need to build a list of Pairs to select from
- so much easier on the memory
- instead loops the iter a random number of times
- and *then* builds a Pair on the iteration where stopped

MasterDuke17/rakudo,rakudo/rakudo,lucasbuchala/rakudo,lucasbuchala/rakudo,nbrown/rakudo,usev6/rakudo,tbrowder/rakudo,tony-o/rakudo,labster/rakudo,softmoth/rakudo,salortiz/rakudo,labster/rakudo,usev6/rakudo,tbrowder/rakudo,tbrowder/rakudo,tony-o/rakudo,MasterDuke17/rakudo,awwaiid/rakudo,awwaiid/rakudo,tony-o/rakudo,MasterDuke17/rakudo,labster/rakudo,tony-o/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,labster/rakudo,jonathanstowe/rakudo,softmoth/rakudo,softmoth/rakudo,sjn/rakudo,awwaiid/rakudo,jonathanstowe/rakudo,jonathanstowe/rakudo,awwaiid/rakudo,Gnouc/rakudo,rakudo/rakudo,MasterDuke17/rakudo,nbrown/rakudo,awwaiid/rakudo,rakudo/rakudo,labster/rakudo,softmoth/rakudo,tbrowder/rakudo,salortiz/rakudo,sjn/rakudo,rakudo/rakudo,salortiz/rakudo,nbrown/rakudo,tbrowder/rakudo,rakudo/rakudo,raydiak/rakudo,lucasbuchala/rakudo,rakudo/rakudo,Gnouc/rakudo,jonathanstowe/rakudo,usev6/rakudo,sjn/rakudo,Gnouc/rakudo,sjn/rakudo,usev6/rakudo,tony-o/rakudo,lucasbuchala/rakudo,usev6/rakudo,salortiz/rakudo,nbrown/rakudo,nbrown/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,salortiz/rakudo,sjn/rakudo,nbrown/rakudo,salortiz/rakudo,labster/rakudo,raydiak/rakudo,Gnouc/rakudo,Gnouc/rakudo,jonathanstowe/rakudo,raydiak/rakudo,softmoth/rakudo,raydiak/rakudo,lucasbuchala/rakudo,tony-o/rakudo