transform the path when packing

[petebacondarwin]

Is it possible to transform the path of each file as it goes into the tarball.
In other words provide a mapping function that changes the path name that is attached to each file as it is added to the archive.

This can be done in the command line tar by using the --transform=expression option (see http://www.gnu.org/software/tar/manual/html_section/transform.html)

I have a need to prefix each file with an extra folder name.

I can't see an obvious way of achieving this without hacking the node-tar library.

[spolu]

This would also be nice to have while extracting

[othiym23]

Closing as a duplicate of #17.