multiple stat endpoint support + moved stat topic to separate frame

.The outgoing stats socket can now be configured to connect to multiple endpoints.  This allows connecting to local stats dumping tools as well as forwarding to an aggregation point if you want to collect stats from multiple meatspace instances.

The message topic has been moved to it's own message frame.

Simple node.js dumper:

var zmq = require('zmq'), sock = zmq.socket('sub');
sock.subscribe("");
sock.bindSync ('tcp://127.0.0.1:9999');

sock.on('message', function(topic, stat) {
    console.log('RECEIVED: topic: %s, stat: %s', topic.toString(), stat.toString());
});