[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
Really? I don't like to pass multiple values as array... Can't really tell you why, I guess that's subjective :-)

My favourite thing would be to go for variables used like here, and use named parameters, as we have discussed this week. Hopefully it'll be included soon in PHP :-)