Changes from Mercurial (hg https://foss.heptapod.net/isa-afp/afp-devel/ default)
Summary
- merge from afp-2021-1
- tuned error messages;
- mention error location when metadata loading fails;
- merged
- even more IsaNet;
- afp metadata/releases: change format to re-add releases swallowed by key-set, remove extra releases;
- more IsaNet
- New entry IsaNet
- re-introduce accidentally reverted changes