Retire UCI_Chess960 option

We don't need that !

We can infere from starting fen string if we are in
a Chess960 game or not. And note that this is a per-position
property, not an application wide one.

A nice trick is to use a custom manipulator (that is an
enum actually) to keep using the handy operator<<() on the
move when sending to std::cout, yes, I have indulged a
bit here ;-)

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

src/position.h

@@ -272,6 +272,7 @@ public:
   // Other properties of the position
   bool opposite_colored_bishops() const;
   bool has_pawn_on_7th(Color c) const;
+  bool is_chess960() const;
 
   // Current thread ID searching on the position
   int thread() const;
@@ -335,6 +336,7 @@ private:
   int castleRightsMask[64];
   StateInfo startState;
   File initialKFile, initialKRFile, initialQRFile;
+  bool isChess960;
   int startPosPlyCounter;
   int threadID;
   StateInfo* st;
@@ -555,6 +557,11 @@ inline bool Position::has_pawn_on_7th(Color c) const {
   return pieces(PAWN, c) & relative_rank_bb(c, RANK_7);
 }
 
+inline bool Position::is_chess960() const {
+
+  return isChess960;
+}
+
 inline bool Position::move_is_capture(Move m) const {
 
   // Move must not be MOVE_NONE !