Hydrilla

improve loading of schema files

make strip_json_comments() exported from module again

add tests for features from version 2 of source package JSON schema

incorporate version 2 of Hydrilla JSON schemas

make it easier to reuse/cache foreign package files when building a Hydrilla source package multiple times

always use APT packages for amd64 architecture

raise a more informative error when a file referenced from index.json is missing

properly handle percent-encoded characters in .deb file names

add missing english translations and verify message texts of raised exceptions in tests

support piggybacking on APT packages