Feature: Parse the complex escape sequence after \\

[sundy-li]

Summary

Description for this feature.

 fn read_escaped_string_text(&mut self, buf: &mut Vec<u8>) -> Result<()> {
        self.keep_read(buf, |f| f != b'\t' && f != b'\n' && f != b'\\')?;
        if self.ignore_byte(b'\\')? {
            // TODO parse complex escape sequence
            buf.push(b'\\');
            self.read_escaped_string_text(buf)?;
        }
        Ok(())
    }