Add tons of builtin helpers and array operations.

object/builtin_rest.go

@@ -7,7 +7,7 @@ func Rest(args ...Object) Object {
 			len(args))
 	}
 	if args[0].Type() != ARRAY_OBJ {
-		return newError("argument to `rest` must be ARRAY, got %s",
+		return newError("argument to `rest` must be array, got %s",
 			args[0].Type())
 	}