Package main implements jarcat, a program to efficiently concatenate .zip files.
Originally this was pretty simple and that was all it could do, over time it's
gained a bunch more features on a more or less as needed basis.
It's now used for most general-purpose zip and tar manipulation in Please, since
the standard tools either differ between implementations (e.g. GNU tar vs. BSD tar)
or introduce indeterminacy, often in regard to timestamps.