LoadCatalog reads a catalog file and returns its contents as a Catalog pointer.

NewEmtpyCatalog return Catalog pointer.

SaveCatalog persists the system catalog as `catalog.db`.

ErrParseCatalogFile means that parsing of the catalog file (json file) failed.

ErrSaveCatalogFile means that saving of the catalog file (json file) failed.

Catalog is the top-level structure for data storage.