Implements consistent hashing that can be used when the number of
server nodes can increase or decrease (like in memcached). The
hashing ring is built using the same algorithm as libketama.

Consistent hashing is a scheme that provides a hash table functionality
in a way that the adding or removing of one slot does not significantly
change the mapping of keys to slots.

WWW: http://pypi.python.org/pypi/hash_ring