Increase pawn king attack weight

Tighter lower bound for pawn attacks so to
activate king safety in some cases like here:

6k1/2B3p1/2Pp1p2/2nPp3/2Q1P2K/P2n1qP1/R6P/1R6 w

Original patch by Chris, further simplified by
Jörg Oster.

Passed both short TC
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 30171 W: 5887 L: 5700 D: 18584

And long TC
LLR: 2.97 (-2.94,2.94) [0.00,6.00]
Total: 20706 W: 3402 L: 3204 D: 14100

bench: 7607562

src/evaluate.cpp

@@ -434,7 +434,7 @@ Value do_evaluate(const Position& pos) {
     {
         ei.kingRing[Them] = b | shift_bb<Down>(b);
         b &= ei.attackedBy[Us][PAWN];
-        ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) / 2 : 0;
+        ei.kingAttackersCount[Us] = b ? popcount<Max15>(b) : 0;
         ei.kingAdjacentZoneAttacksCount[Us] = ei.kingAttackersWeight[Us] = 0;
     }
     else