Function builtin_strptime 

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

Parse a character string into a POSIXct date-time using a format specification.

@param x character string to parse @param format strptime-style format string @param tz timezone name (default: UTC) @return a POSIXct object