[Feature request] Layer caching

[chrisgorgo]

It would be superbly beneficial if the docker2api tool provided support for caching layers. In other words, the amount of data that needs to be transferred would be minimized in case of small incremental updates or when the image on docker hub did not change since last time docker2aci was run. This would be especially useful in context of big images that include many binary dependencies (common in containerized academic applications). The cache could be stored in the home folder by default.

[lucab]

As most of appc, docker2aci is currently not in active development mode so this new feature is not currently on the radar. However, we'll gladly accept PRs from any interested contributors!