Rewrite Rhai function dispatching

examples/simple_fn.rs

@@ -1,7 +1,9 @@
 extern crate rhai;
-use rhai::{Engine, FnRegister};
+use rhai::{Any, Engine, RegisterFn};
 
 fn add(x: i64, y: i64) -> i64 {
+    println!("Adding: {}", x + y);
+
     x + y
 }
 
@@ -9,8 +11,17 @@ fn main() {
     let mut engine = Engine::new();
 
     engine.register_fn("add", add);
+    engine
+        .call_fn_raw(
+            "add".to_owned(),
+            vec![
+                &mut (Box::new(3i64) as Box<Any>),
+                &mut (Box::new(5i64) as Box<Any>),
+            ],
+        )
+        .expect("FAIL");
 
-    if let Ok(result) = engine.eval::<i64>("add(40, 2)") {
-       println!("Answer: {}", result);  // prints 42
-    }
+    //if let Ok(result) = engine.eval::<i64>("add(40, 2)") {
+    //    println!("Answer: {}", result); // prints 42
+    //}
 }