Git based incremental backups #31

Incremental backups are the next step to creating a backup as small as possible, and a good compromise between usability and efficiency is using a Git based system, similar to Fast Backup. I would say the standard we should aim for is a backup that is able to be opened by Git client like Github Desktop.

Features it should have:

• Use Git features to save incremental snapshots of the world, saving space
• Optional push to a user configured repository
• Use intelligent strategies to also gain a speed improvement over traditional Chronos Backups

The speed improvement is less straight forward. While normally, we could compare the region file with its previous version to see if it needs updating, but for Chronos, the region file is pruned, meaning before we could do a comparison, we have to prune it, which wastes compute. To get around this, we should compute the pre-prune hash and save it in a database in the generated repository, and this will be read by the next backup to figure out whether the file changed at all and whether replacing (and thus also pruning) will be necessary. This database will then be replaced after the backup to prepare for the next backup.