Function addScaled

addScaled(a, b, scale, dst?): Vec3
Adds two vectors, scaling the 2nd; assumes a and b have the same dimension.
Parameters
- a: Vec3
  Operand vector.
- b: Vec3
  Operand vector.
- scale: number
  Amount to scale b
- Optional dst: Vec3
  vector to hold result. If not passed in a new one is created.
Returns Vec3
A vector that is the sum of a + b * scale.