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- Export ``ImageHistoryItem`` through the package entrypoint.
- Add ``image_size`` property to ``PlatformImage`` and ``Manifest`` classes.
- Add ``short_digest`` property to all data classes that have a ``digest`` property. This is meant
to mimic the short digests shown on Docker Hub.
- Add ``non_empty_history`` property to ``ImageConfig`` class, to retrieve a list of only non-empty
layers. This is a convenience method to retrieve a list of history items that will nicely line up
with the list of downloadable layers.
- Add ``clean_created_by`` property to ``ImageHistoryItem`` class, to centralise efforts for
providing "nice" displays of layer information.