1.0.21

• Provide DoubleEndedIterator and ExactSizeIterator implementations for anyhow::Chain to assist in custom rendering of cause chains (#45)

  let chain = err.chain();
  if chain.len() > 1 {
      eprint!("[[root cause]] ");
  }
  for err in chain.rev() {
      eprintln!("{}", err);
  }