refactor examples to use print(x) instead of putstrln(itos(x))

examples/factorial.lamb

@@ -1,4 +1,4 @@
 factorial(0) -> 1.
 factorial(n) -> n * factorial(n - 1).
 
-putstrln(itos(factorial(10))).
+print(factorial(10)).

examples/listlength.lamb

@@ -1,4 +1,4 @@
 sum([]) -> 0.
 sum(x::xs) -> 1 + sum(xs).
 
-putstrln(itos(sum([1, 2, 3]))).
+print(sum([1, 2, 3])).

examples/listsum.lamb

@@ -1,4 +1,4 @@
 sum([]) -> 0.
 sum(x::xs) -> x + sum(xs).
 
-putstrln(itos(sum([1, 2, 3]))).
+print(sum([1, 2, 3])).