mk: everyo / someo — predicate-style relations

(everyo rel l): every element of l satisfies the unary relation rel.
(someo rel l): some element does. Both compose with intarith and other
predicate-shaped goals:
  (everyo (fn (x) (lto-i x 10)) (list 1 5 9))    -> succeeds
  (someo  (fn (x) (lto-i 100 x)) (list 5 50 200)) -> succeeds

10 new tests, 310/310 cumulative.

lib/minikanren/relations.sx

@@ -140,3 +140,19 @@
     (conde
       ((nullo l1) (nullo l2))
       ((fresh (a d a-prime d-prime) (conso a d l1) (conso a-prime d-prime l2) (rel a a-prime) (mapo rel d d-prime))))))
+
+(define
+  everyo
+  (fn
+    (rel l)
+    (conde
+      ((nullo l))
+      ((fresh (a d) (conso a d l) (rel a) (everyo rel d))))))
+
+(define
+  someo
+  (fn
+    (rel l)
+    (conde
+      ((fresh (a d) (conso a d l) (rel a)))
+      ((fresh (a d) (conso a d l) (someo rel d))))))