implement the quote special form.

that was easy. (if it is correct.)

onwards to list! (which is trickier, because it has a variable number of
arguments and we have to call evalo on all of them, in sequence.
mhh... that kind of sounds like we need a listo?)

scm/evalo.scm

    (conde
     [(symbolo expr)
      (lookupo expr env val)]
     [(fresh (e)
        (== `(quote ,e) expr)
        (== e val))]
     [(fresh (x body)
        (== `(lambda (,x) ,body) expr)
        (== `(closure ,x ,body ,env) val))]