Implement a method to extract a single file

[tinovyatkin]

Thank you for the module!

I want to use this module to inspect tarballs (like Docker OCI images) and in most cases need to extract one or two specific files (i.e. index.json) so it will be very useful if a method for that can be provided (like Entry.asBytes).

tar CLI can do so like tar -x -O -f something.tar index.json