Shrink sequencer table

Integrate TT_MOVE step into the first state. This allows to
avoid the first call to next_phase() in case of a TT move.

And use overflow detection instead of the bunch of STOP_XX
states to detect end of moves.

No functional change.

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

src/movepick.h

@@ -47,7 +47,7 @@ private:
   void score_captures();
   void score_noncaptures();
   void score_evasions();
-  void next_phase();
+  void generate_next();
 
   const Position& pos;
   const History& H;