Tweak kingAttackersCount and KingAttackWeights

Use the whole kingRing for pawn attackers instead of only the squares directly
around the king. This tends to give quite a lot more kingAttackersCount, so to
compensate and to avoid raising the  king danger too fast we lower the values
in the KingAttackWeights array a little bit.

STC:
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 51892 W: 10723 L: 10369 D: 30800
http://tests.stockfishchess.org/tests/view/5af6d4dd0ebc5968e652428e

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 24536 W: 3737 L: 3515 D: 17284
http://tests.stockfishchess.org/tests/view/5af709890ebc5968e65242ac

Credits to user @xoroshiro for the idea of using the kingRing for pawn attackers.

How to continue? It seems that the KingAttackWeights[] array stores values
which are quite Elo-sensitive, yet they have not been tuned with SPSA recently.
There might be easy Elo points to get there.

Closes #1597

Bench: 5282815

AUTHORS

@@ -118,3 +118,4 @@ Tom Vijlbrief (tomtor)
 Torsten Franz (torfranz)
 Uri Blass (uriblass)
 Vince Negri
+xoroshiro

src/evaluate.cpp

@@ -89,7 +89,7 @@ namespace {
   constexpr Value SpaceThreshold = Value(12222);
 
   // KingAttackWeights[PieceType] contains king attack weights by piece type
-  constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 78, 56, 45, 11 };
+  constexpr int KingAttackWeights[PIECE_TYPE_NB] = { 0, 0, 77, 55, 44, 10 };
 
   // Penalties for enemy's safe checks
   constexpr int QueenSafeCheck  = 780;
@@ -281,7 +281,7 @@ namespace {
         else if (file_of(pos.square<KING>(Us)) == FILE_A)
             kingRing[Us] |= shift<EAST>(kingRing[Us]);
 
-        kingAttackersCount[Them] = popcount(attackedBy[Us][KING] & pe->pawn_attacks(Them));
+        kingAttackersCount[Them] = popcount(kingRing[Us] & pe->pawn_attacks(Them));
         kingAttacksCount[Them] = kingAttackersWeight[Them] = 0;
     }
     else