Add more archivers

[elboletaire]

Add more archivers/packers other than cbz:

• RAW: Just export images to folders.
• ZIP: Same as CBZ, but using zip extension (not sure if this is useful really).
• EPUB: There are some CBZ to epub converters like KCC, consider if it's a good feature, or it's better to keep it as external.
• CBR: Could not find any RAR wrinting library for go, so it'll have to wait probably.

[elboletaire]

I've just seen a similar application where they were treating CBR like CBZ files... just zipping the files and renaming them as CBR is not the way to go. CBR files should be RAR compressed archives, not zip archives. On one side I understand why they did this, on the other I think is completely useless (and probably is done just to get more attention).

At the same time, I don't think there are devices that only support CBR and not CBZ files, so I'm not really sure this feature is really needed at all (and if you want the file to have a .cbr extension, you can just rename the resulting file).