Function write_stream 

fn write_stream(
    MdStream: &MdStream<'_>,
    buf: &mut Vec<u8>,
    default: Option<Style>,
    indent: usize,
    formatter: Option<&(dyn Fn(&str, &mut Vec<u8>) -> Result<()> + 'static)>,
) -> Result<()>

Write the buffer, reset to the default style after each, optionally with a formatter for code blocks