bug#69305: outline-minor-mode for tabulated-list-mode

[Juri Linkov]

> So if you were to use one of these as inspiration (or as a library
> directly), I'd strongly recommend using `taxy', as that's what it's
> designed for.
> [...]
> Let me know if I can help facilitate a solution using it, or help anyone
> work with the API.

Thanks for proposing help, but for inspiration I'm using
my own package https://github.com/link0ff/emacs-ee
It's much more powerful than anything I have seen so far.
But on the other hand, it became so unmanageable
that I semi-abandoned it due to its overly complexity.

Is your package more light-weight than mine?  I doubt it ;-)

This is why I proposed to do the same with minimal changes relying on
existing core packages tabulated-list-mode and outline-minor-mode that
already handle 95% of required functionality.

What remains to do is just to fill the rest 5%.  In addition to the
first patch, there will be 2-3 equally small patches that will
complete functionality equivalent to the said packages.