Move pretty printer into boot.dst

examples/primes.dst

@@ -0,0 +1,14 @@
+# Return an array of primes. This is a trivial and extremely naive algorithm.
+
+(defn primes
+ "Returns a list of prime numbers less than n."
+ [n]
+ (def list [])
+ (for [i 2 n]
+  (var isprime? true)
+  (def len (length list))
+  (for [j 0 len]
+   (def trial (get list j))
+   (if (zero? (% i trial)) (varset! isprime? false)))
+  (if isprime? (array-push list i)))
+ list)