bug#22336: 25.0.50; cl-generic.el features are not documented in ELisp manual

[Stefan Monnier]

> ':method' is in the doc string, which for me was a clear sign it
> should be documented.

I consider that the docstring should be a "reference" documenting as
much of the supported behavior as possible, whereas the manual should be
more accessible (give context and examples) and less exhaustive.

> Such dynamically-updated doc string would be very good to have, I
> think, but I needed to work with what was there, and of course
> couldn't use the kind of intimate knowledge of the implementation that
> you have.

I definitely understand that, and I thank you for doing this work.


        Stefan