Add support for ACLs

I'm wrapping up the dump archive reader and don't know how to present ACL information. In this case the ACL information is stored after the data so I can't simply add it to the archive-specific Entry class - it will only be available after the end of the data stream is reached.

More generally this problem occurs with other extended attributes, e.g., SELinux labels. You can also have this problem with MacOS specific streams, e.g., the finder stream.

One possibility is returning an ArchiveEntry for the extended attributes. It can have a isMetadata() method to indicate it's extended attributes. This has a huge downside though since legacy code would replace the file contents with the extended attributes so we would want an explicit acknowledgement that the code is prepared to handle it, e.g., by a constructor flag.

Is there a better way to handle this?