[FEATURE] Concatenate list fields

__Tasks:__

- [x] test coverage
- [x] gather feedback for my changes
- [x] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | parts of #129 
| Doc           | none
Actually I would prefer that, because it's also typesafe. However, I will merge that now, since we have to make progress. Maybe we can add the fluent interface approach later, and offer both ways (fluent interface and the constructor) later.