public BonusFrame(Roll roll1, Roll roll2)
 {
     _rolls = new [] { roll1, roll2 };
     _sum   = _rolls.Sum(roll => roll.RollValue);
 }
 public BonusFrame(Roll roll)
 {
     _rolls = new [] { roll };
     _sum   = roll.RollValue;
 }
 public StrikeFrame()
 {
     _roll = new Roll(10);
 }
 public SpareFrame(Roll roll1)
 {
     _rolls = new Roll[] { roll1, new Roll(10 - roll1.RollValue) };
 }
 public OpenFrame(Roll roll1, Roll roll2)
 {
     _rolls   = new Roll[] { roll1, roll2 };
     _rollSum = _rolls.Sum(roll => roll.RollValue);
 }