Add a subcommand to manage the cache

[sbordeyne]

Due to the filesystem backend using hive, it's not human readable, hence hard to manually go in the cache to remove entries, or debug what is happening.

One option would be to not use hive for storage, and instead rely on the filesystem itself (which can have portability issues), the other would be to add a subcommand to manage the cache, list items in the cache, purge it, or even add items manually in there.