Add yaw() to Transform.

src/core.rs

@@ -479,6 +479,17 @@ impl From<&dyn PointLike> for (i32, i32) {
     }
 }
 
+pub trait TransformExt {
+    fn yaw(&self) -> Angle;
+}
+
+impl TransformExt for Transform {
+    fn yaw(&self) -> Angle {
+        let forward = self.right();
+        Angle::Radians(forward.y.atan2(forward.x))
+    }
+}
+
 pub trait GlobalTransformExt {
     fn yaw(&self) -> Angle;