Accumulate collections of values and records.
Fix up some warnings in the Sandvich string transformer.
Extract out the separator duplication in the string accumulators.
Pull out the element builders into a separate Builder interface to remove duplication.
Rename Serializer to RekordSerializer, and AccumulatorBuilder to Serializer.
Move the DomXmlSerializer element and text node creation into their own class.
Rename Serializer.Builder::nest to "map".
Reuse the DomXmlBulder in the DomXmlSerializer.
Rename the Builder to Constructor, along with its methods.