Add Scope to API. Move todo to github

examples/reuse_scope.rs

@@ -0,0 +1,14 @@
+extern crate rhai;
+use rhai::{Engine, Scope};
+
+fn main() {
+    let mut engine = Engine::new();
+    let mut scope: Scope = Vec::new();
+
+    if let Ok(_) = engine.eval_with_scope(&mut scope, "var x = 4 + 5".to_string()) { } else { assert!(false); }    
+
+    if let Ok(result) = engine.eval_with_scope(&mut scope, "x".to_string()).unwrap().downcast::<i32>() {
+       println!("result: {}", result);
+    }
+}
+