Roadmap initiative: async fundamentals

[tmandry]

This issue tracks the steps for setting up a new initiative in the async vision roadmap.
Please read the instructions for owning an initiative.

Top-level goal: #242 Async fn everywhere
Initiative owner: @tmandry

Each initiative should have a landing page, linked to from the roadmap. This can be a page on this website or a dedicated repo.

For in-progress initiatives the landing page should include, or have pointers to:

• Goals and impact of the initiative
• Milestones
• Design notes and documentation (this may be sparse in the beginning)
• Links to any organizing tools, such as a project board
• The initiative owner
• The current set of stakeholders and the area(s) they represent
• Notes on how to get involved
• For landing pages not on this website, a link back to the overall roadmap

For making a dedicated repo, it's recommended to use this initiative template as a starting point.

Remember, you don't have to do these all at once!

This issue can be closed when all of the above items are complete.