void OnCollisionEnter2D(Collision2D col)
{
// Objects with specific collision routines are (e.g. finishes) called here.
// These each have a script component deriving from the Collidable class,
// and override PlayerHit() to make this work.
Collidable collidable = col.gameObject.GetComponent <Collidable>();
if (collidable != null)
{
collidable.PlayerHit(this);
return; // Stop processing here.
}
canJump = true;
}