Function builtin_encoding 

fn builtin_encoding(
    args: &[RValue],
    _: &[(String, RValue)],
) -> Result<RValue, RError>

Report the encoding of character strings.

Returns “unknown” for pure-ASCII strings, “UTF-8” for non-ASCII. miniR is UTF-8 everywhere, so this simply checks for non-ASCII bytes.

@param x character vector @return character vector of encoding names