class Protobuf::Rpc::Client

client.on_success {|res| ... }
client = Client.new(:service => WidgetService)

Callback is called regardless of :async setting.
If this callback is called, failure_cb will NOT be called.
successful response from the service when it is returned.
Set a success callback on the client to return the

def on_success(&success_cb)
  @connector.success_cb = success_cb
end