Invalid link for Smit's algorithm

[VephoVandenberg]

The link for 'safer' implementation is invalid. Don't you think that this resource is valid, for that task: https://www.pbr-book.org/3ed-2018/Shapes/Basic_Shape_Interface or this https://www.scratchapixel.com/lessons/3d-basic-rendering/minimal-ray-tracer-rendering-simple-shapes/ray-box-intersection.html#:~:text=time%3A%2010%20mins.-,Ray%2DBox%20Intersection,1%20and%20b%3D%2D1.

[cgyurgyik]

I am no longer maintaining this, but am happy to review pull requests.