function pow(out, a, b) {
    ln(out, a);
    scale$2(out, out, b);
    exp(out, out);
    return out;
  }
Calculate the scalar power of a unit quaternion.

@param {quat} out the receiving quaternion
@param {ReadonlyQuat} a quat to calculate the exponential of
@param {Number} b amount to scale the quaternion by
@returns {quat} out