support {input: "existing.tar"} ?

[bosky101]

more of a feature request. my use case is being able to add to an existing tar.

i'm yet to find a node module that allows opening existing tar file.

// this would be cool
var cloned = new Tar ( {input: "existing.tar" , output:"next.tar" });
cloned.append(...)
// this should also work
var udpated = new Tar ( {input: "existing.tar" , output:"existing.tar" });
updated.append(...)

if this is already possible, a demo in examples / test cases will be great.

~B