Scale history bonus based on score - beta delta

[kelseyde]

Story so far:

Score of Calvin DEV vs Calvin: 553 - 600 - 1133  [0.490] 2286
...      Calvin DEV playing White: 435 - 112 - 596  [0.641] 1143
...      Calvin DEV playing Black: 118 - 488 - 537  [0.338] 1143
...      White vs Black: 923 - 230 - 1133  [0.652] 2286
Elo difference: -7.1 +/- 10.1, LOS: 8.3 %, DrawRatio: 49.6 %