Remove the Accumulator type parameter from Kollector.
Use a Pattern object instead of `String::replaceAll`.
Rename `Kollector` to `Serializer`. Because seriously.
Move serialization classes to the `serialization` package.
Make the transformer constructors static in ComposingTransformerTest.
Move the nested accumulation into the Accumulator.
Keys have names. Make it explicit.
Explicitly test serializing transformed keys.
Move the accumulation behaviour to the keys.
Ensure that transformed rekord keys are serialized according to the original structure.
Remove a now-unnecessary @SuppressWarning.
Fix accumulator method parameters.
Move the `finish` method to the Serializer.
Remove redundant code from DomXmlAccumulator.
Create a common interface for accumulating single values or maps.