title: Rust doc test with async function #[tokio-test]
body: <p>It seems one cannot use <code>#[tokio-test]</code> for test async functions in the Rust doc test?</p>
  <p>For now I have to write an async main function and tag it with <code>#[tokio-main]</code> and call <code>test_fn().await</code> in it to let some async function run during <code>cargo test --doc</code>.</p>
  <p>Is there some other better ways to allow doc tests run as if it is a normal test function, for example with <code>#[tokio-test]</code>? Also it would be nice if the tag <code>#[tokio-test]</code> can be shown in the doc, so users can copy the doc and use it as a test directly in their project. (And this probably can be done like <code>##[tokio-test]</code>?)</p>