message: implement Error trait for bip44 related Errors
diff: //! ```
  use hdpayload::{Path};
  -use std::{fmt, result};
  +use std::{fmt, result, error};
  #[cfg(feature = "generic-serialization")]
  use serde;
  @@ -74,6 +74,7 @@ impl fmt::Display for Error {
  }
  }
  }
  +impl error::Error for Error {}
  pub type Result<T> = result::Result<T, Error>;
  