Full XCI (Key Area + XCI) and reversible XCZ

[alucryd]

Hi again, it seems no-intro started adopting the new Full XCI format, which is the old XCI we know but prepended with the key area [0]. The rewrite branch of nxdumptool can be used to generate such files. This format will most likely quickly gain traction, and being able to go back and forth between Full XCI and XCZ would be awesome.

As it stands, it seems nsz will need an update to read such files, as trying to compress one raises an OSError: OSError: Not a valid HFS0 partition b'\x00\x00\x00\x00' @ fffc. So I guess this would be a double feature request. I might very well try to make a PR over the weekend if time allows it, at least to address reading these Full XCI files.

[0] https://switchbrew.org/wiki/XCI#CardKeyArea

[alucryd]

Had some time to tackle the first part: #148