a sublist is when one list is found verbatim inside another list.
determines whether a list is a sublist of another. if it can, it
returns the location where it was found. otherwise, returns
say sublist::index(<d e f>, <a b c d e f g>); # should print 3
finds all sublist indexes and returns a list of them. returns
none are found.
# ↓ should print 3 and 7
.say for sublist::indices(<d e f>, <a b c d e f and d e f g>);