During some recent personal programming, I needed a function to slice a list
into pieces: Given a list of sub-list lengths, and an input list to be sliced,
return a list of sub-lists of the requested lengths. For instance:, slicing the
list (1 2 2 3 3 3) into sub-lists of lengths (1 2 3) returns the list of
sub-lists ((1) (2 2) (3 3 3)). Extra list elements at the end of the input list
are ignored, missing list elements at the end of the input list are returned as
null lists.

Your task is to write a program that slices lists into sub-lists according to a
specification of sub-list lengths. When you are finished, you are welcome to
read or run a suggested solution, or to post your own solution or discuss the
exercise in the comments below.