message: Support #[repr(packed)] in #[derive(H5Type)]
diff: @@ -149,7 +149,8 @@ fn impl_trait(
  if fields.is_empty() {
  panic!("Cannot derive H5Type for empty structs");
  }
  - find_repr(attrs, &["C"]).expect("H5Type requires #[repr(C)] for structs");
  + find_repr(attrs, &["C", "packed"])
  + .expect("H5Type requires #[repr(C)] or #[repr(packed)] for structs");
  let types = pluck(fields.iter(), |f| f.ty.clone());
  let fields = pluck(fields.iter(), |f| f.ident.clone().unwrap());
  let names = fields.iter().map(|f| f.to_string()).collect::<Vec<_>>();
  @@ -166,7 +167,8 @@ fn impl_trait(
  if fields.is_empty() {
  panic!("Cannot derive H5Type for empty tuple structs");
  }
  - find_repr(attrs, &["C"]).expect("H5Type requires #[repr(C)] for structs");
  + find_repr(attrs, &["C", "packed"])
  + .expect("H5Type requires #[repr(C)] or #[repr(packed)] for structs");
  let names = (0..fields.len()).map(|f| f.to_string()).collect::<Vec<_>>();
  let types = pluck(fields.iter(), |f| f.ty.clone());
  impl_compound(ty, ty_generics, &index, &names, &types)
  