ADDITIONS
- feat: make FormatCode public
- fix: read FormatCode into FileHeader and validate
IMPROVEMENTS
- feat: add AllowEmptyIndividualName
- fix: reject records after FileControl is parsed
- fix: ensure IndividualName is populated (non-blank, non-zero) for some SEC codes
- test: trying out .rtf file
- test: checking out missing_file_control.rtf