v1.0.0b

• Cluster.remove_zone now raises ValueError on attempt to remove a
  non-existent zone.
• Cluster.remove_node and RendezvousHash.remove_node now raise
  ValueError on attempt to remove a non-existent node.
• Support for custom hash functions retracted for 1.0.0 milestone.
• murmur_seed keyword argument renamed to seed for Cluster and
  RendezvousHash __init__ methods.