Add eval cache infrastructure

With this patch series we want to introduce a per-thread
evaluation cache to store node evaluation and do not
rely anymore on the TT table for this.

This patch just introduces the infrastructure.

No functional change.

src/evaluate.h

@@ -20,6 +20,7 @@
 #if !defined(EVALUATE_H_INCLUDED)
 #define EVALUATE_H_INCLUDED
 
+#include "misc.h"
 #include "types.h"
 
 class Position;
@@ -30,6 +31,16 @@ extern void init();
 extern Value evaluate(const Position& pos, Value& margin);
 extern std::string trace(const Position& pos);
 
+const int TableSize = 262144;
+
+struct Entry {
+  Key key;
+  Value value;
+  int16_t margins[2];
+};
+
+struct Table : HashTable<Entry, TableSize> {};
+
 }
 
 #endif // !defined(EVALUATE_H_INCLUDED)