Exercise 2.27: Modify your reverse
procedure of Exercise 2.18 to produce a deep-reverse procedure
that takes a list as argument and returns as its value the list with its
elements reversed and with all sublists deep-reversed as well.  For example,


(define x 
  (list (list 1 2) (list 3 4)))

x
((1 2) (3 4))

(reverse x)
((3 4) (1 2))

(deep-reverse x)
((4 3) (2 1))