Update examples

This updates the examples to showcase the scope of anthem’s feature set.
New examples are added concerning placeholders, hiding predicates, and
simplifications related to integer variables.

examples/permutations.lp

@@ -1,3 +1,5 @@
+#show p/2.
+
 {p(1..n, 1..n)}.
 
 :- p(X, Y1), p(X, Y2), Y1 != Y2.
@@ -8,5 +10,3 @@ q2(Y) :- p(_, Y).
 
 :- not q1(X), X = 1..n.
 :- not q2(Y), Y = 1..n.
-
-#show p/2.