[EPIC] Integrate threats into history table

An interesting technique is to add threats to the history table and use that information as part of move order scoring. An example implementation from `pawnoccio` https://github.com/JonathanHallstrom/pawnocchio/compare/1d6fcd13..54826286

This will require incremental updating in our `Board` so that we can properly track threats without having to recompute them for each position.
