Update issues, merge pull requests and do a roadmap for SpinalDoc-RTD

Documentation is at the same time somewhat easy, mildly boring, most of the time harmless and very important.

I had lunch a few times with @Dolu1990 since the year start and one thing that seems clear is that PR and issue management takes a lot of his time. For the spinal language repo it is well invested time in my opinion, but for this doc it's a bit of waste of expertise. So in an effort to reduce the "administrative" load for him and other more experienced contributors, I'm going to try to reduce the backlog of issues and PR for this repo.

Also, I propose that this issue is used to track the roadmap of things to do for this doc (if you have a better idea, like using the wiki, let me know below).

Roadmap:

• ask for status on any issue older that a year
• integrate PR what are easily mergeable
• tag issue with relevant tags
• ask for status on any PR that is not mergeable
• move all PR still Work-In-Progress to draft
• close unused branches
• update requirements.txt
• after PR are mostly merged, wrap the .rst to 80 chars (ideally with a tool) so it's more readable (to discuss)
• do a roadmap for the doc based on the feedback and things discovered along the way