Move piece values in piece.h / piece.cpp

Where they belong.

Note that array PieceValueMidgame[] and PieceValueEndgame[]
are now declared extern in the header and moved in piece.cpp
so to avoid allocate the array each time the header is
included !

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>

src/position.cpp

@@ -71,10 +71,16 @@ struct PieceLetters : std::map<char, Piece> {
     }
 };
 
+
 ////
-//// Variables
+//// Constants and variables
 ////
 
+/// Bonus for having the side to move (modified by Joona Kiiski)
+
+static const Score TempoValue = make_score(48, 22);
+
+
 Key Position::zobrist[2][8][64];
 Key Position::zobEp[64];
 Key Position::zobCastle[16];