Add multicast support to Rinda::Ring*
This patch adds multicast support to Rinda::Ring.
If the addresses list for Rinda::RingServer or Rinda::RingFinger contain a multicast address then a multicast socket will automatically be created and used.
Rinda::RingServer#initialize was changed to accept three arguments, but in a backwards-compatible manner.
Rinda::RingServer#shutdown was added.
Tests for socket creation were added.