Anchored bishops

Anchored bishops

Reduce the "bad bishop" penalty when the bishop is protected by
one of our pawns, as it may indicate that the bishop has found
a safe spot outside the pawn chain.

STC:
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 176942 W: 34142 L: 33696 D: 109104
Ptnml(0-2): 3129, 20422, 40919, 20876, 3125
http://tests.stockfishchess.org/tests/view/5e6f61aae42a5c3b3ca2e62d

LTC:
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 42252 W: 5615 L: 5322 D: 31315
Ptnml(0-2): 308, 3881, 12500, 4084, 353
http://tests.stockfishchess.org/tests/view/5e701382e42a5c3b3ca2e661

closes https://github.com/official-stockfish/Stockfish/pull/2587

Bench: 4963440