This library allows reading and writing gzip-compressed JSON catalog
files, which can be used to store GPG, PKCS-7 and SHA-256 checksums for
each file. It provides equivalent functionality to the catalog files
supported in Microsoft Windows. Unlike Microsoft catalog files which are
a signed manifest of hashes, a Jcat file is a manifest of signatures.
This means it's possible (and positively encouraged) to modify the .jcat
file to add new signatures or replace existing ones.
