Add `?suf` argument to `pretty_*` functions

[sim642]

This would be convenient for adding a trailing newline.
Of course this can easily be added by other means but given that the non-pretty output functions already have it, it would also be consistent.

[Leonidas-from-XIV]

@sim642 Thanks for the report. While I understand the value of being consistent I always thought that ?suf was a bit of an odd and somewhat unrelated thing. I personally think it shouldn't really exist, as it is pretty trivial to add a suffix to the data after writing to it.

What's the usecase that you have in mind where ?suf would make sense?

[sim642]

My use case was simply switching from the non-pretty functions to the pretty ones and having to do a bit more to get things to work.

I guess there's a related consistency aspect: to_buffer, to_output and to_file have no pretty versions. And out of those to_file by default uses a newline for suf.

[Leonidas-from-XIV]

I agree that there's some potential for consistency…

The reason why to_file uses \n as ?suf is due to practical inconsistency, since text files often are supposed to end with a training newline, so making it '' by default would break a lot of current users and most would need to add ~suf:'\n' instead.