Assorted tweaks from DON

Mainly renames and some little code style improvment,
inspired by looking at DON sources:

https://github.com/erashid/DON

No functional change.
Faster handling of king captures in Position::see

Another SEE speed up that passed the SPRT short TC test!

LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 81337 W: 15060 L: 14745 D: 51532

No functional change.
merge fix try 1