score first derivative of the loglikelihood for each observation.
params : ndarray
parameter at which score is evaluated
scale : None or float
If scale is None, then the default scale will be calculated. Default scale is defined by self.scaletype and set in fit. If scale is not None, then it is used as a fixed scale.
score_obs : ndarray, 2d
The first derivative of the loglikelihood function evaluated at params for each observation.