King tropism

Bonus for each square that we attack in the flank where the opponent
king is. Squares that we attack twice and are not protected by an enemy
pawn count double.

Passed STC:
http://tests.stockfishchess.org/tests/view/577dfca60ebc5972faa166b8
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 48373 W: 9832 L: 9481 D: 29060

And LTC:
http://tests.stockfishchess.org/tests/view/577e77870ebc5972faa166df
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 8881 W: 1408 L: 1255 D: 6218

Bench: 7577046