Release 0.8.6

This is for collaborative release notes and related stuff.

Force pushes are disabled on this branch so we don't clobber each other's commits.

Might be a good idea to post in chat if you're creating a section, to avoid duplication of effort.

Please see the README for how to use the new markdown image processing, and the noob guide for an example of it in production.
tl;dr put a single png or lossless webp in the same directory as index.md