message: Implement std::error::Error for flat::Error
diff: @@ -1451,6 +1451,32 @@ impl From<Error> for ImageError {
  }
  }
  +impl fmt::Display for Error {
  + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
  + match self {
  + Error::TooLarge => write!(f, "The layout is too large"),
  + Error::NormalFormRequired(form) => write!(
  + f,
  + "The layout needs to {}",
  + match form {
  + NormalForm::ColumnMajorPacked => "be packed and in column major form",
  + NormalForm::ImagePacked => "be fully packed",
  + NormalForm::PixelPacked => "have packed pixels",
  + NormalForm::RowMajorPacked => "be packed and in row major form",
  + NormalForm::Unaliased => "not have any aliasing channels",
  + }
  + ),
  + Error::WrongColor(color) => write!(
  + f,
  + "The chosen color type does not match the hint {:?}",
  + color
  + ),
  + }
  + }
  +}
  +
  +impl error::Error for Error {}
  +
  impl PartialOrd for NormalForm {
  /// Compares the logical preconditions.
  ///
  