Reorder and reorganize the README for better utility

We can move "Implemented" and Dropped to a history index. The main view should show what is interesting. The priority for that is
1. What is under review
2. What is in draft

But why is Draft even there are all? Once you tell people about it, it is out for review, even if you don't think you want comments about it. If you want to share something with just a few people, you should do that via other channels.

Open the repository README and compare its current sections with the requested organization. Move Implemented and Dropped into a history index, prioritize under-review items before drafts, and verify that the main view highlights current proposals.

Written by the indexing model from the issue text.