// segment between the squares s1 and s2 (excluding s1 but including s2). If the
// given squares are not on a same file/rank/diagonal, it returns s2. For instance,
// between_bb(SQ_C4, SQ_F7) will return a bitboard with squares D5, E6 and F7, but
// between_bb(SQ_E6, SQ_F8) will return a bitboard with the square F8. This trick
// allows to generate non-king evasion moves faster: the defending piece must either
// interpose itself to cover the check or capture the checking piece.
// segment between the squares s1 and s2 (excluding s1 but including s2). If the
// given squares are not on a same file/rank/diagonal, it returns s2. For instance,
// between_bb(SQ_C4, SQ_F7) will return a bitboard with squares D5, E6 and F7, but
// between_bb(SQ_E6, SQ_F8) will return a bitboard with the square F8. This trick
// allows to generate non-king evasion moves faster: the defending piece must either
// interpose itself to cover the check or capture the checking piece.