added struct literals

examples/math/main.bl

@@ -28,6 +28,12 @@ fn unit_function() {
   let a: I32 = 4;
 }
 
+fn returns_user(): User {
+    return User{
+        id: 4,
+    };
+}
+
 fn main(): I32 {
     add(4, subtract(5, 2))
 }