deprecated:
  typedef unsigned char BYTE

  Bitboard64 (const char16_t quarters[4])
  Bitboard64 (const char32_t halfs[2])
  bool state (int byte, int bit) const
  void invert (const int m, const int n)
  void set (const int index, bool state)
    -> replaced by  void set (int index)  and  void reset (int index)
  void set (const int m, const int n, const bool state)

added:
  void set (const int index)
  void reset (const int index)