bug#41868: [PATCH] Add project-clean-up command

[Juri Linkov]

>> +(defcustom project-spare-buffers-regexps
>> +  '("\\*Help\\*")
>
> Perhaps also call this project-buffer-spare-conditions?

I think the suffix ‘-regexps’ is fine.  The problem is that
the word “spare” has no reference to the related command name
‘project-kill-buffers’.  Maybe better would be something like
‘project-kill-buffers-ignore-regexps’ or

> Or something like that. Point is, no tie the name to regexps, for easy
> extension into having functions in that list as well.

For functions it's easy to add a separate variable like
‘project-kill-buffers-ignore-functions’.