Add support for simple OOB Round Robin load balancing

[kul]

It would be great to provide some simple Round Robin Load balancing OOB.Like

var options =
{
balance:
{
'localhost:'localhost:8181',
'localhost':'localhost:8182'
}
};

var proxyServer = httpProxy.createServer(options);
proxyServer.listen(80);

[Marak]

I'm not sure if it's a good idea to include balancing logic in the core module. Balancing should be the responsibility of another library.

I did add a simple http load balancing example to the project. :-)

https://github.com/nodejitsu/node-http-proxy/blob/master/examples/balancer/simple-balancer.js