Use default rust directory structure for tests

tests/while_loop.rs

@@ -0,0 +1,15 @@
+extern crate rhai;
+
+use rhai::Engine;
+
+#[test]
+fn test_while() {
+    let mut engine = Engine::new();
+
+    if let Ok(result) = engine.eval::<i64>("let x = 0; while x < 10 { x = x + 1; if x > 5 { \
+                                            break } } x") {
+        assert_eq!(result, 6);
+    } else {
+        assert!(false);
+    }
+}