Move to_char() and to_string() to notation

Where they better belong.

Also, this removes '#include <string>' from types.h, which reduces the amount of code to compile (every
translation unit includes types.h).

No functional change.

src/bitboard.h

@@ -21,6 +21,7 @@
 #ifndef BITBOARD_H_INCLUDED
 #define BITBOARD_H_INCLUDED
 
+#include <string>
 #include "types.h"
 
 namespace Bitboards {

src/notation.h

@@ -32,4 +32,17 @@ const std::string move_to_uci(Move m, bool chess960);
 const std::string move_to_san(Position& pos, Move m);
 std::string pretty_pv(Position& pos, int depth, Value score, int64_t msecs, Move pv[]);
 
+inline char to_char(File f, bool tolower = true) {
+  return char(f - FILE_A + (tolower ? 'a' : 'A'));
+}
+
+inline char to_char(Rank r) {
+  return char(r - RANK_1 + '1');
+}
+
+inline const std::string to_string(Square s) {
+  char ch[] = { to_char(file_of(s)), to_char(rank_of(s)), 0 };
+  return ch;
+}
+
 #endif // #ifndef NOTATION_H_INCLUDED

src/position.cpp

@@ -30,6 +30,7 @@
 #include "rkiss.h"
 #include "thread.h"
 #include "tt.h"
+#include "notation.h"
 
 using std::string;
 

src/types.h

@@ -405,14 +405,6 @@ inline bool opposite_colors(Square s1, Square s2) {
   return ((s >> 3) ^ s) & 1;
 }
 
-inline char to_char(File f, bool tolower = true) {
-  return char(f - FILE_A + (tolower ? 'a' : 'A'));
-}
-
-inline char to_char(Rank r) {
-  return char(r - RANK_1 + '1');
-}
-
 inline Square pawn_push(Color c) {
   return c == WHITE ? DELTA_N : DELTA_S;
 }
@@ -446,11 +438,4 @@ inline bool is_ok(Move m) {
   return from_sq(m) != to_sq(m); // Catches also MOVE_NULL and MOVE_NONE
 }
 
-#include <string>
-
-inline const std::string to_string(Square s) {
-  char ch[] = { to_char(file_of(s)), to_char(rank_of(s)), 0 };
-  return ch;
-}
-
 #endif // #ifndef TYPES_H_INCLUDED