Allow reusing Vector2 instance

[implicit-invocation]

https://github.com/aloisdeniel/Comora/blob/master/Sources/Comora/Camera.cs#L190

Can you modify these to use public static void Transform(ref Vector2 position, ref Matrix matrix, out Vector2 result) and avoid some GC?

[aloisdeniel]

Sure I'll push an update very soon. That makes sense.