New MINOR release 03.21.00

Changes since 03.20.00:

- feat: lmap fanout plugin
- feat(lmap): Convenience plugins for system tags

- fix: Do noting in CopyRegisterDecorator::doPreRead
- fix: exception handling from ReadAnyGroup::accept
- fix: compiler error on clang

- feat: add user type as value type
- chore: add C++ concepts

- test: versionNum after exception within readAny