Detect (and remove) files that aren't available on Itch servers (older version of games)

[TheFrenchGhosty]

Currently, itchiodl will download every new file as if the older one don't exist:

• if a file with the same name exist, it will overwrite it
• if a file with a different name exist, it will just download the new file and "ignore" the existing file

This is a bit of a problem, in the sense that everytime a game update, you will more than likely keep the older version.

lgogdownloader (the main GOG.com downloader) "solves" that with --check-orphan function that will check and reports (only reports, it won't do anything to them) the files that exist that aren't available to download anymore (which is, almost all the time: older versions).

itchiodl definitely needs something like that considering how many "thing" someone can have with the bundles.

Something that can delete those older files would be even better, but a "detector" would be a good start.

PS: thanks (again) for itchiodl!