bug#63861: [PATCH] pp.el: New "pretty printing" code

[Stefan Monnier]

>> Or maybe, I should leave `pp` alone and add a new `pp-region`
>> function instead instead of combining two different calling conventions
>> on a single function?
>
> That might be better, indeed, both for documentation and for usage.

Done.  That also leads to fewer visible changes, so it's good (I just
kept `pp-buffer` instead of adding `pp-region`).

I pushed the result (after fixing the test problems with option B).
Thanks,


        Stefan