Reset weights after a resampling step.

def reset_weights(self):
        """Reset weights after a resampling step. 
        """
        if self.fk.isAPF:
            lw = (rs.log_mean_exp(self.logetat, W=self.W)
                  - self.logetat[self.A])
            self.wgts = rs.Weights(lw=lw)
        else:
            self.wgts = rs.Weights()