Allow directories to be transfered via ZIP compatible to original imlementation

[rugk]

See magic-wormhole/magic-wormhole#396 (comment)

Yes, unfortunately I believe the Rust implementation maintainers chose a different packaging format for some reason (that's incompatible with v1 directory-transfer to a python or Haskell implementation) based implementations since they both use zip).

If that's the case, why not introduce a switch to choose the version?
Or the version or so?

[meejah]

Note that I could have been wrong above, I didn't double-check -- but yeah if this implementation is indeed using Tar, then ideally defaulting to "zip" (with a tar option) would be ideal and allow for maximum interoperation.

[felinira]

Just as context, this was the rationale for initially not supporting this format. #137

I would generally prefer not having to write temporary files to the disk and rather move on with the much more flexible dilation based protocol for multi-file transfer.