derive Copy for Direction

While similar enum like `Corner` implement `Copy` trait but `Direction` does not. Since this enum is simple it should make sense to derive this.

Suggested in #634

src/layout.rs

@@ -14,7 +14,7 @@ pub enum Corner {
     BottomLeft,
 }
 
-#[derive(Debug, Hash, Clone, PartialEq, Eq)]
+#[derive(Debug, Hash, Clone, Copy, PartialEq, Eq)]
 pub enum Direction {
     Horizontal,
     Vertical,