- Anyhow works with any error type that has an impl of `std::error::Error`,
  including ones defined in your crate. We do not bundle a `derive(Error)` macro
  but you can write the impls yourself or use a standalone macro like
  [err-derive].
  [err-derive]: https://crates.io/crates/err-derive
  ```rust
  #[derive(Error, Debug)]
  pub enum FormatError {
      #[error(display = "invalid header (expected {:?}, got {:?})", expected, found)]
      InvalidHeader {
          expected: String,
          found: String,
      },
      #[error(display = "missing attribute: {}", _0)]
      MissingAttribute(String),
  }
  ```

//!
//! - Anyhow works with any error type that has an impl of `std::error::Error`,
//!   including ones defined in your crate. We do not bundle a `derive(Error)`
//!   macro but you can write the impls yourself or use a standalone macro like
//!   [err-derive].
//!
//!   [err-derive]: https://crates.io/crates/err-derive
//!
//!   ```
//!   # const IGNORE: &str = stringify! {
//!   #[derive(Error, Debug)]
//!   pub enum FormatError {
//!       #[error(display = "invalid header (expected {:?}, got {:?})", expected, found)]
//!       InvalidHeader {
//!           expected: String,
//!           found: String,
//!       },
//!       #[error(display = "missing attribute: {}", _0)]
//!       MissingAttribute(String),
//!   }
//!   # };
//!   ```