Add roadmap with development plans in website

[florence-bockting]

Description

This PR adds a roadmap with information about current and planned development plans (wrt loo).
The roadmap shall appear on the loo website and be accessible for the community.

ToDos

• update the PR number in NEWS.md
• remove the roadmap.html file currently included for easier review.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.50%. Comparing base (7991145) to head (16527cd).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #396   +/-   ##
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  Coverage   92.50%   92.50%           
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  Files          31       31           
  Lines        3107     3107           
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  Hits         2874     2874           
  Misses        233      233           

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[florence-bockting]

Hi, I worked on a roadmap for the loo package.
What do you think about it @jgabry, @avehtari, @VisruthSK? Any ideas for topics to change, remove, add?

The following link uses githack and will open the .html (without the Stan style website) for easier review.
When you click the link the first time, it will ask you whether you trust the source.

preview of roadmap

On the website it could then look as follows (here just the upper part of the document is shown):

[github-actions]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if 16527cd is merged into master:

• ✔️loo_function: 1.36s -> 1.36s [-1.18%, +1.67%]
• ✔️loo_matrix: 1.49s -> 1.49s [-1.39%, +0.94%]
  Further explanation regarding interpretation and methodology can be found in the documentation.

[VisruthSK]

This is very cool!

I think it might be nice to link to the milestones so people could see all the PRs/issues associated with each? Similarly for open issues/PRs.

My one concern is that this page won't be maintained as we move things from In Progress to Planned--maybe we only highlight completed topics?

[florence-bockting]

To link it with milestones in the PR/Issues is a good idea. That's nice.

Regarding the labeling "In Progress" and "Planned": I agree that it might be a bit annoying to actually keep track of this nuance. We could remove the "status" information, then we don't need to worry about that.

[jgabry]

Yeah I think this is really great as long as it's easily maintainable without having to constantly remember to update it. We used to have a roadmap for the entire Stan project that was public but it was hard to keep it up to date. If this is just pulling from GitHub milestones and things that like then that's better, but any prose about any of the plans will have to be updated manually.