message: Use eprintln instead of println to send error messages to stderr
diff: @@ -671,7 +671,7 @@ impl Subscription {
  for m in r.iter() {
  if let Err(e) = handler(m) {
  // TODO(dlc) - Capture for last error?
  - println!("Error in callback! {:?}", e);
  + eprintln!("Error in callback! {:?}", e);
  }
  }
  });
  