v2.1.0: DDF Spec change: 🔠 UPPERCASE IDENTIFIERS ARE NOW LEGAL
feat: allow uppercase letters in identifiers
feat: add CSV byte-level format checking (BOM, CRLF, UTF-8 encoding)
Add test cases and fixtures to validate csv files
E_CSV_ROW_BAD: make error message more descriptive and add column counts
Make explicit error message when incorrect identifier is found (was EOF)