Function append_pax_record 

pub fn append_pax_record(
    output: &mut Vec<u8>,
    keyword: &PaxKeyword,
    value: &[u8],
) -> Result<(), FramingWriteError>

Appends one PAX extended-header record without block padding to output.

keyword must be nonempty and cannot contain =. value is copied verbatim and may contain arbitrary bytes.