message: Fix consumer processing comments
diff: @@ -428,7 +428,7 @@ impl Consumer {
  }
  }
  - /// Process a single message for a pull-based consumer.
  + /// Process a batch of messages.
  pub fn process_batch<R, F: FnMut(&Message) -> R>(
  &self,
  batch_size: usize,
  @@ -484,7 +484,7 @@ impl Consumer {
  Ok(rets)
  }
  - /// Process a single message for a pull-based consumer.
  + /// Process a single message.
  pub fn process<R, F: Fn(&Message) -> R>(&self, f: F) -> io::Result<R> {
  if self.cfg.durable_name.is_none() {
  return Err(Error::new(
  