bug#53945: saveplace should save the buffer's mark list too

[emacsq]

> But are you sure that the package with the name "saveplace"
> is a suitable place to save the mark ring?

Since marks are also places in the file it's not unnatural if
saveplace saves other places too.  .

> For example, saveplace.el is optimized to not save the location
> when point is at the beginning of the buffer. So in such cases
> the mark ring will not be saved too.

I guess it's not hard to disable this optimization if marks are
also saved.

> What if someone would like to save only the mark ring,
> but not to save locations in files?

This can be solved with a new option if the need ever arises,
and the option may not even affect the saving part (who cares
if the current location is saved along with the marks, just
one more number), only the restoring of the position is skipped
when the file is opened.