Use int instead of Value for history related stats.

history related scores are not related to evaluation based scores.
For example, can easily exceed the range -VALUE_INFINITE,VALUE_INFINITE.
As such the current type is confusing, and a plain int is a better match.

tested for no regression:

STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 43693 W: 7909 L: 7827 D: 27957

No functional change.

Closes #1070

src/search.h

@@ -44,7 +44,7 @@ struct Stack {
   Move excludedMove;
   Move killers[2];
   Value staticEval;
-  Value history;
+  int history;
   int moveCount;
 };