Add Support for Partitions

[slinga-homebrew]

Add support for device partitions. Notably SGC does not work correctly with the Floppy Disk Drive (FDD). The first partition works, the second is invisible. Unfortunately Jo Engine does not make visible the partitions as far as I can tell.

[johannes-fetz]

johannes-fetz/joengine#40 is fixed

All functions supports partition

New functions:
jo_backup_save_file_contents_on_partition()
jo_backup_get_file_partition()

[slinga-homebrew]

Thank you Johannes. I will make a debug build and have someone with the floppy drive test.

[slinga-homebrew]

I got feedback that the code had some issues. One complaint was that the code double displayed files. I will review the commit and see if I can figure out what's going on. Unfortunately I do not own the Saturn Floppy Disk Drive

[johannes-fetz]

I have a lot of accessories for the saturn, but not the FDD (almost 200€ on eBay). We have to get one or we will code blindly