Releasing Horowitz v2.2.0.
Changes mainly involved minor improvements in late move reductions and quiet moves ordering in search. A very basic hash table was also implemented for storing pawn structures in evaluation.
Score of horowitz-new vs horowitz-old: 34 - 19 - 47 [0.575]
... horowitz-new playing White: 18 - 10 - 22 [0.580] 50
... horowitz-new playing Black: 16 - 9 - 25 [0.570] 50
... White vs Black: 27 - 26 - 47 [0.505] 100
Elo difference: 52.5 +/- 49.9, LOS: 98.0 %, DrawRatio: 47.0 %