[META] Pain Point Tracker

[Stebalien]

This is where I'm going to keep a list of known pain points with tempfile v3 that can't be fixed without breaking changes. I don't know if we'll ever have a v4, but if we do, we can revisit everything on this list:

• TempDir implements AsRef<Path> making it easy to accidentally drop it.
• A file name prefix can contain a slash. May be fixable in a minor version with a warning?
• Temporary directories are created with the default mode unlike temporary files which are created with 0o600. Ideally temporary directories would use restrictive permissions by default.

[marcospb19]

I'd expect the #59 fix to require a major version update, it's not obvious to users whether that's a bug or intended behavior, so that should be assumed as breaking IMHO.

EDIT: that is, if the fix is to make that function panic.