Old issues related to documentation

There are several that suggest better exercise documentation: approaches, mentoring notes, etc.

- #660
- #652
- #644
- #264
- #303

I don't disagree with what they say, but (based on past experience, preparing for 48in24) I believe that both the following statements are true:

- Approaches are a valuable addition to Exercism, and it would be good to have more of them
- If done well, approaches are a slog to write and a slog to review. Anyone who tries to create lots of them quickly loses enthusiasm.

Others are of course free to write what they wish, but in the coming months my focus will be on the learning syllabus.