Add support for Skopeo docker-archive and OCI-formatted container images #29
Description
Skopeo's https://github.com/containers/skopeo docker-archive: format is not exactly the docker save format and uses links for layer.tar tarballs ... See https://github.com/containers/skopeo/blob/cc3ddf4804995ab69606885c83a9990b84d1de36/docs/skopeo.1.md#L38
OCI images should be supported too. See https://github.com/containers/image/blob/56ddc22a8b0b1cef6fc1c5f321285fbde7f4274b/docs/containers-transports.5.md#oci-archivepathtag and https://github.com/opencontainers/image-spec/blob/daf51542d53813621913dde9bf438bd9c1fe32c8/spec.md