Change history reduction in LMR to be a full ply.

STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 9829 W: 2142 L: 1998 D: 5689

LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 27162 W: 4802 L: 4692 D: 17668

Bench: 7284120

Resolves #53
Cap evaluation based null move extra reduction to three plies

It's a zero elo patch, and a reasonable safeguard against uncontrolled extreme reductions.

STC:
ELO: -0.08 +-2.0 (95%) LOS: 46.9%
Total: 40000 W: 6728 L: 6737 D: 26535

LTC:
ELO: -0.14 +-1.8 (95%) LOS: 44.0%
Total: 40000 W: 5557 L: 5573 D: 28870

Bench: 7201830
Merge branch 'master' into cleanup
fix beta < VALUE_KNOWN_WIN

It should be alpha < VALUE_KNOWN_WIN. Using beta here is very wrong:
* if we do null move at PV nodes, the condition on beta makes no sense
* if beta = VALUE_KNOWN_WIN (admittedly a rare case), then performing
null search is ok, in fact. it's the alpha floor that matters.
* makes code more self-documenting (and add a comment anyway), becuase
it's the alpha floor that matters, and we don't want to allow fake win
scores to be created on the back of it.

bench 7203047