vdukhovni authored Jan 03, 2021 and Marge Bot committed Jan 09, 2021

- Renamed new "update function" to "operator" from synopses
- More accurate divergence conditions.
- Fewer references to the Tree structure in examples, which
  may not have the definition close-by in context in other
  modules, e.g. Prelude.
- Improved description of foldlM and foldrM
- More detail on Tree instance construction
- Misc fixes