Stepbacks/reverses the buffer.
        Optional arguments:
        * append=False - If True, appends the data onto the buffer;
                        else, it just steps the index back.

def stepback(self, append=False):
        """
        Stepbacks/reverses the buffer.
        Optional arguments:
        * append=False - If True, appends the data onto the buffer;
                        else, it just steps the index back.
        """
        if append:
            data = self._buffer[self._index - 1]
            self._buffer.append(data)
        else:
            self._index -= 1