Support exhibitfiles to set files that need to be "exhibited" in the current workspace; fix a typo

[myhsia]

Support exhibitfiles to set files that need to be "exhibited" in the current workspace

Some users merge a README.md file, for example, into a *.dtx file.
Once they change the markdown file, they should modify the source *.dtx file.

But l3build won't move the generated (unpacked) markdown file to the main directory (corresponding to currentdir in l3build-variables), and users usually need to keep the markdown file (or other files) in the main directory so that it can be displayed on the GitHub repository homepage.

So, a variable exhibitfiles is added: after unpack is executed, the enumerated text files will be copied from unpackdir to currentdir; and certainly, these exhibitfiles will be cleaned after l3build clean.

Fix a typo

In l3build.dtx, line 2249: \loggingoutput is misspelled in the macro environment.

[cfr42]

doesn't this assume currentdir is maindir, which may often not be the case?

[cfr42]

I think this would be better accommodated by implementing existing requests for additional hooks e.g. unpackinit_hook().

[myhsia]

I think this would be better accommodated by implementing existing requests for additional hooks e.g. unpackinit_hook().

Actually, in order to handle this problem, I used a "trick"

function docinit_hook()
  cp(ctanreadme, unpackdir, currentdir)
  return 0
end

in some of my packages. The docinit_hook actually also works, but I think it would be better to provide a more friendly interface for users.

[myhsia]

Anyone to review it? @davidcarlisle @josephwright @cfr42

[cfr42]

you move the files into maindir but remove them from currentdir.

but I am not sure sure l3build should be removing files outside the build directory and I am not sure how this is supposed to work when you have multiple projects in subdirectories of a single repo or, say, bundles. (but I'm a bit unclear re. the concept of a bundle.)

since ctan want to have the readme at the top level, I'm not quite seeing how it makes sense to have it in a .dtx. don't you then effectively have to always distribute two copies?

[cfr42]

but you need to ask the maintainers to consider this rather than me ;).