pub fn look_at(dir: Vector2<S>, up: Vector2<S>) -> Matrix2<S> {
        Matrix2::look_at_stable(dir, up.x * dir.y >= up.y * dir.x)
    }
Create a transformation matrix that will cause `unit_x()` to point at
`dir`. `unit_y()` will be perpendicular to `dir`, and the closest to `up`.
src/matrix.rs