Append a value to the stats list

        Parameters
        ----------
        value : float
            The value to add

def append(self, value):
        """
        Append a value to the stats list

        Parameters
        ----------
        value : float
            The value to add
        """
        self.count += 1

        if self.count == 1:
            self.old_m = self.new_m = value
            self.old_s = 0
        else:
            self.new_m = self.old_m + (value - self.old_m) / self.count
            self.new_s = self.old_s + (value - self.old_m) * (value - self.new_m)

            self.old_m = self.new_m
            self.old_s = self.new_s