Add for pinned pawns half of the standard rank based threat bonus.
STC:
LLR: 2.97 (-2.94,2.94) [0.00,5.00]
Total: 44010 W: 9987 L: 9635 D: 24388
http://tests.stockfishchess.org/tests/view/
5b58aa780ebc5902bdb88c7a
LTC:
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 29475 W: 5089 L: 4847 D: 19539
http://tests.stockfishchess.org/tests/view/
5b58b56c0ebc5902bdb88f37
Closes https://github.com/official-stockfish/Stockfish/pull/1701
Bench:
4503866