Directory::read_entry_boxed plus common abstraction make_boxed

[phip1611]

This adds a function to Directory to get directory entry information as boxed/owned values. This is done similar to File::get_boxed_info [commit1]. Unfortunately, the code is almost identical. I tried to create a new commonly shared abstraction [commit2]. However, it is not that easy to let it compile successfully. I'm seeking for advice.

Checklist

• Sensible git history (for example, squash "typo" or "fix" commits). See the Rewriting History guide for help.
• Update the changelog (if necessary)

[phip1611]

This just left it's draft state.

Do you like the make_boxed abstraction?

[phip1611]

I'm really looking forward to bumping the MSRV soon. Again, I had to alter my PR because of that 😀 @nicholasbishop @GabrielMajeri 7ce93f1

[phip1611]

Any update here, @nicholasbishop?

I need it for #472 by the way.

[nicholasbishop]

Code looks good to me. One remaining thing though, read_entry_boxed should get a changelog entry.

[phip1611]

Code looks good to me. One remaining thing though, read_entry_boxed should get a changelog entry.

I updated the changelog and I take your words as approval.