ZbyszekMM

## Describe your changes We still do not have a description of complex aggregations ("the #AGG helper") in the docs. I ignore the checklist below, all checks are "N/A". ##...

## Describe your changes Added a bullet on enrichments in the "Why Nu" section. I missed it out in the current version. Additionally some small text bugs corrections.

## Describe your changes ## Checklist before merge - [ ] Related issue ID is placed at the beginning of PR title in \[brackets\] (can be GH issue or Nu...

 

A set of unrelated small corrections + complete rewrite of the single-side-join component + deeper corrections of previousValue component. Here, the `groupBy` parameter name was changed to `key`.

## Describe your changes