Resolve public identifiers and remap system identifiers
Description
This module implements draft 0.4 of John Cowan's XML Catalog (formerly known as XCatalog) see
(<https://www.oasis-open.org/committees/entity/specs/cs-entity-xml-catalogs-1.0.html>) Catalogs may
be written in either SOCAT or XML syntax. XML::Catalog will assume SOCAT syntax if the catalog is
not in well-formed XML syntax.