add $and and $c (for contracts)

```racket
;; $and
(~define ($and lst ($ (list lst-0 lst-1))) '(0 1))
(check-equal? lst '(0 1))
(check-equal? lst-0 0)
(check-equal? lst-1 1)
(~define ($and (~vs ($and lst0 lst_0) lst1) (~vs ($list lst0-0) ($list lst1-0 lst1-1)))
         (values '(lst0-0) '(lst1-0 lst1-1)))
(check-equal? lst0 '(lst0-0))
(check-equal? lst_0 '(lst0-0))
(check-equal? lst1 '(lst1-0 lst1-1))
(check-equal? lst0-0 'lst0-0)
(check-equal? lst1-0 'lst1-0)
(check-equal? lst1-1 'lst1-1)

;; $c
(~define ($c x real?) 3.14159)
(check-equal? x 3.14159)
(check-exn exn:fail:contract?
           (λ ()
             (~define ($c x real?) "not a real number")
             (void)))
(~define ($c ($list f0) (list/c (-> real? real?)))
         (list (λ (x) x)))
(check-equal? (f0 3.14159) 3.14159)
(check-exn exn:fail:contract?
           (λ ()
             (f0 "not a real number")))
```