Benchmark against other implementations

[svenstaro]

We should benchmark this against a few other implementations to figure out where we are:

• https://github.com/brandonpelfrey/Fast-BVH
• https://embree.github.io/
• https://github.com/rkruppe/beevage.rs
• https://github.com/ruuda/convector
• https://github.com/kvark/collision-rs/tree/master/src/dbvt
• https://github.com/lohedges/aabbcc
• https://github.com/sebcrozet/ncollide/tree/master/ncollide_geometry/partitioning

[svenstaro]

All other implementations are now unmaintained except for maybe Embree.