Improved error message for missing required flags: now list all missi…

…ng required flags for better user guidance. (#340)

Issue: #215

Fixing typo in README

Bump go.mod to v2

Add test GHA

Fix error propagation from @ failures.

Really fixes #185.

Generated .String() functions now return the correct value.

Fixes #201.

Added newline to example in README

Fix envars with numbers.

Fixes #138.

Fix bug where --help doesn't terminate.

--help exits with 0 (fixes #136), added UsageWriter() and ErrorWriter…

…() (fixes #137)

These writer functions should be preferred over .Writer().