Add plane intersection to Raycast object

[pvdosev]

This adds a method for the Raycast class to be able to intersect with planes. I tried to follow the style of the other intersection methods, let me know if anything doesn't look right! The math is the same as described here: https://math.stackexchange.com/questions/4402134/determining-plane-intersection-with-a-ray

[gordonnl]

Thanks a lot!