add unarchiver example

[jm33-m0]

Hi Matt, thanks for the great work!

I noticed there's no Unarchive function in v4 yet, and the documentation is incomplete and hard to follow, so I wrote a small program that invokes your extractor API to automatically identify the format and unarchive tarballs.

Please check the code and point out where I need to improve. It can serve as an example for users who seek a quick solution from this project.

[mholt]

Thanks for this; I like the idea of posting an example instead of prescribing one way to do it in the code itself.

I have a few suggestions on how to tweak this but I will have to come back and write those up later.

I suppose this might resolve #311.

[mholt]

Does this example take into account #391?

[jm33-m0]

Does this example take into account #391?

In fact, my code doesn't retain the file/dir permissions. So I guess it will "solve" #391.

[mholt]

Gotcha. This is a good start, but I think file mode bits (permissions, etc) are important, so we might need to include those in a proper example.

[jm33-m0]

I have updated the code with necessary changes to address the directory permission issue, and I also added code to handle symlinks.

[mholt]

Thank you! However, I don't think we should be providing an actual program, just an example in the docs.

I'm actually about the archive this repository, but we can continue this discussion over in mholt/archives if you would like.