message: multithread example - wasn't in parallel
  Before it was awaiting for each iteration to be done, therefore not in parallel.
  I changed it to be in parallel
diff: @@ -32,12 +32,13 @@ async fn main() {
  create_keyspace(session.clone()).await;
  create_table(session.clone()).await;
  - for i in 0..20 {
  + let futures : Vec<tokio::task::JoinHandle<()>> = (0..20).into_iter().map(|i| {
  let thread_session = session.clone();
  tokio::spawn(insert_struct(thread_session, i))
  - .await
  - .expect("thread error");
  - }
  +
  + }).collect();
  +
  + let _responses = futures::future::join_all(futures);
  select_struct(session).await;
  }
  