Add ability to load wider range of EOL separated text files

## Background
Currently, `.option("is_text", "true")` is limited to ASCII UTF-8 files.
EOL separators allow us to treat a file as a fully variable-length file.

## Feature
Implement `is_text` through variable-length readers to
- [ ] Allow other charsets for ASCII
- [ ] Allow specifying EOL character and escape
- [ ] Allow EBCDIC with code pages
- [ ] Allow multisegment and hierarchical records