bug#64185: proposal for new function: copy-line

[Eli Zaretskii]

> From: Zachary Kanfer <zkanfer@gmail.com>
> Date: Fri, 23 Jun 2023 01:46:27 -0400
> Cc: Juri Linkov <juri@linkov.net>, 64185@debbugs.gnu.org, me@eshelyaron.com
> 
> Is there a standard to use numbers as the values, rather than, say, symbols? 
> It seems more readable
> to look at an option of '(old new last), for example, rather than '(-1 0 1).

Numbers are much easier for users to use as values of options, so we
should prefer them when they do the job.  A number can also express
more than just those 3 possibilities, so it's more flexible in this
case.

> I also like the added tests!

That's always welcome, TIA.