v0.0.57
* Add method BaseModel.hashes().
* Re-introduce the swh.core dependency in swh.model[cli]
* Add support for skipping large contents in from_disk.
* Add to_model() method to from_disk.{Content,Directory}, to convert to canonical model objects.
* Take the value of MerkleNode.data into account to compute equality.
* Add method MerkleNode.iter_tree, to visit all nodes in the subtree of a node.
* Add from_datetime and from_iso8601 constructors for TimestampWithTimezone.
* Make attributes name and email of Person optional.