implementation of the top-k streaming algorithm

 The Statistics::TopK module implements the top-k streaming algorithm, also
 know as the "heavy hitters" algorithm. It is designed to process data streams
 and probabilistally calculate the k most frequent items while using limited
 memory.
 .
 A typical example would be to determine the top 10 IP addresses listed in an
 access log. A simple solution would be to hash each IP address to a counter
 and then sort the resulting hash by the counter size. But the hash could
 theoretically require over 4 billion keys.
 .
 The top-k algorithm only requires storage space proportional to the number of
 items of interest. It accomplishes this by sacrificing precision, as it is
 only a probabilistic counter.