We now avoid the `<T>` in the page title. We refer to `Rc` and `Arc`
as reference-counted shared pointers that allow access to data from
multiple places or threads.

- Avoid time-specific statements (“recently”, “today”, …).

- Move details such as “RPIT” to the speaker notes.

- More links to our slides as well as community documentation.

- Formatting fixes

This moves all non-trivial examples in the async part of the course to
self-contained Rust files. This ensures that we can test them in CI.

The 1-day classes are sometimes taught to people who haven’t taken
Rust Fundamentals, or who have taken it a while ago. So it seems nice
to remind everybody that questions are very welcome.

Bullet points makes it looks more like, well, a slide!

This keeps the original structure, but removes 7 lines of code.

This removes a nested import (which I find hard to read) and removes
an unnecessary type annotation.

This reduces the vertical space needed by the example, thus making it
easier to keep on the screen while refactoring it.