Added sketch for HTTP load balancer

Actually no, because you still check for NULL return value in order to return "500 Failed" status. One liner improvement would be:

```c
    } else if ((nc->proto_data = ns_connect(nc->mgr,
               s_http_backends[chosen].host_port, ev_handler)),
               nc->proto_data->flags & NSF_BAD_CONNECTION) {
      /* Connection to backend failed */
      ns_printf(nc, "%s", "HTTP/1.1 500 Failed\r\nContent-Length: 0\r\n\r\n");
    } else {
```

So, if I understood correctly, if the connection/socket fails to be created we'll return 500 Failed. While if the socket is created but fails to connect to the backend (or any other error that happens asynchronously), we'll silently close the connection. IMHO we should have a more consistent response, since this failure here could be a transient error, like being out of `fd`.