Get a unit vector tangent at a relative position on the curve. In case any sub curve does not implement its tangent derivation, 2 points a small delta apart will be used to find its gradient which seems to give a reasonable approximation
name  type  arguments  description 

t  number 
The relative position on the curve, [0..1]. 

out  Phaser.Math.Vector2  <optional> 
A vector to store the result in. 
Vector approximating the tangent line at the point t (delta +/ 0.0001)