Import C++11 branch

Import C++11 branch from:

https://github.com/mcostalba/Stockfish/tree/c++11

The version imported is teh last one as of today:
6670e93e50

Branch is fully equivalent with master but syzygy
tablebases that are missing (but will be added with
next commit).

bench: 8080602

src/position.h

@@ -170,12 +170,11 @@ public:
   uint64_t nodes_searched() const;
   void set_nodes_searched(uint64_t n);
   bool is_draw() const;
-  int rule50_count() const;
   Score psq_score() const;
   Value non_pawn_material(Color c) const;
 
   // Position consistency check, for debugging
-  bool pos_is_ok(int* step = NULL) const;
+  bool pos_is_ok(int* step = nullptr) const;
   void flip();
 
 private:
@@ -348,10 +347,6 @@ inline int Position::game_ply() const {
   return gamePly;
 }
 
-inline int Position::rule50_count() const {
-  return st->rule50;
-}
-
 inline uint64_t Position::nodes_searched() const {
   return nodes;
 }