Use default rust directory structure for tests

tests/bit_shift.rs

@@ -0,0 +1,25 @@
+extern crate rhai;
+
+use rhai::Engine;
+
+#[test]
+fn test_left_shift() {
+    let mut engine = Engine::new();
+
+    if let Ok(result) = engine.eval::<i64>("4 << 2") {
+        assert_eq!(result, 16);
+    } else {
+        assert!(false);
+    }
+}
+
+#[test]
+fn test_right_shift() {
+    let mut engine = Engine::new();
+
+    if let Ok(result) = engine.eval::<i64>("9 >> 1") {
+        assert_eq!(result, 4);
+    } else {
+        assert!(false);
+    }
+}