IPv6 support

[snoj]

Modified Gossiper and PeerState to use address and port for naming instead of old way.
Set Gossiper.peer_name and PeerState.name as a read only attributes.

[snoj]

I wasn't able to run the tests as I kept getting the below error. Might be my install though.

   uncaught undefined: Error: Cannot find module 'peer_state'
    at Function.Module._resolveFilename (module.js:338:15)
    at Function.Module._load (module.js:280:25)
    at Module.require (module.js:362:17)
    at require (module.js:378:17)
    at Object.<anonymous> (/path/to/node-gossip/test/peer_state.test.js:1:79)
    at Module._compile (module.js:449:26)
    at Object.Module._extensions..js (module.js:467:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Module.require (module.js:362:17)