Other intersection structures (plane, sphere)

[JulianRuiseco]

Hey.

Thank you very much for making this. We have been creating a wrapper for this project for Babylonjs, and the results are just fantastic.

https://github.com/tlaukkan/rust-ray-intersect-js

I am wondering if you would like a bit of help with the BVH repo. I noticed that you set up a great structure for adding more intersection objects. If I write a plane, and sphere intercept structure, would you be open to merging them into the project?