add to tk_rap

examples/test_mul_fixed.slg

@@ -0,0 +1,22 @@
+fn print(msg: string) #[builtin(Print)] {}
+fn println(msg: string) { print(msg + "\n") }
+
+fn mul(left: int, right: int) -> int {
+    if left == 0 or right == 0 {
+        0
+    } else {
+        left * right
+    }
+}
+
+fn main() {
+    if mul(10,2) == 20 {
+        println("test 1 passed")
+    }
+    if mul(3,2) == 6 {
+        println("test 2 passed")
+    }
+    if mul(0,2) == 0 {
+        println("test 3 passed")
+    }
+}