Increment the counter (overflow rolls back to 0).

def increment(self):
        '''Increment the counter (overflow rolls back to 0).'''

        for i in xrange(len(self._counter) - 1, -1, -1):
            self._counter[i] += 1

            if self._counter[i] < 256: break

            # Carry the one
            self._counter[i] = 0

        # Overflow
        else:
            self._counter = [ 0 ] * len(self._counter)