public CollisionPair(CollisionShell a, CollisionShell b, Vec2 force)
 {
     this.a        = a;
     this.b        = b;
     this.userData = force;
 }
 public void Remove(CollisionShell Shell)
 {
     shellList.Remove(Shell);
 }
 public CollisionPair(CollisionShell a, CollisionShell b)
 {
     this.a = a;
     this.b = b;
 }
 public void Add(CollisionShell Shell)
 {
     shellList.Add(Shell);
 }
 public void Remove(CollisionShell Shell)
 {
     shellList.Remove(Shell);
 }
 public void Add(CollisionShell Shell)
 {
     shellList.Add(Shell);
 }
 public CollisionPair(CollisionShell a, CollisionShell b, Vec2 force)
 {
     this.a = a;
     this.b = b;
     this.userData = force;
 }
 public CollisionPair(CollisionShell a, CollisionShell b)
 {
     this.a = a;
     this.b = b;
 }