message: Fix todo comments
diff: /// Reserved formats
  let reserved = fun (format : Format) => fun (default : Repr format) =>
  - // TODO: set to `default` during readback
  + // TODO: set to `default` during serialisation
  format;
  /// Deprecated formats
  let deprecated = fun (format : Format) => fun (default : Repr format) =>
  - // TODO: set to `default` during readback
  + // TODO: set to `default` during serialisation
  format;
  