Faster and simplified threat eval

Add a bonus according if the attacking
pieces are minor or major.

Passed both short TC
LLR: 2.96 (-2.94,2.94) [-1.50,4.50]
Total: 13142 W: 2625 L: 2483 D: 8034

And long TC
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 18059 W: 3031 L: 2844 D: 12184

bench: 7425809
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
Loosened trigger condition for king safety

Reduce eval discontinuity becuase now we kick in
king safety evaluation in many more cases.

Passed both short TC:
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 8708 W: 1742 L: 1613 D: 5353

And long TC:
LLR: 2.95 (-2.94,2.94) [0.00,6.00]
Total: 6743 W: 1122 L: 990 D: 4631

bench: 6835416
Merge remote-tracking branch 'upstream/master'