shar is specifically mentioned in the footer, with the drawback that it's really an arbitrary shell scipt. ptar is also mentioned, and seems rather nice. It's also way better documented[0] though with glaring holes e.g. how does it deal with non-UTF8 file content (it's not clear whether file size or delimiters is relevant, and why you'd have a closing delimiter if the filesize rules), it also specifies file names as UTF8 or ASCII, neither of which is sufficient to handle the full breadth of possible file names.
[0] https://github.com/jtvaughan/ptar/blob/master/FORMAT.md