Differential backups

[jesjimher]

Hi, first of all, thanks for such a useful piece of software!

Just a suggestion, when databases are big, storing a full dump for each backup is not very efficient. Hard links help with storage efficiency, but it's still not enough. In my case, every database dump is about 700 MB. But if I just do a diff between two different dumps, file size is about 4-5 MB at most. It looks like there's a lot of potential in storing just differences between database dumps, instead of storing a full dump every time.

Thanks!