Document internal cleanup of linebreaks by decode-xml

[TobiasNx]

e.g. handle-generic-xml OR decode-xml are deleting linebreaks and other signs (?)
was: https://metafacture.org/playground/?flux=%22https%3A//repository.tugraz.at/oai2d%22%0A%7C+open-oaipmh%28metadataPrefix%3D%22lom%22%29%0A%7C+as-lines%0A%7C+print%0A%3B%0A

becomes: https://metafacture.org/playground/?flux=%22https%3A//repository.tugraz.at/oai2d%22%0A%7C+open-oaipmh%28metadataPrefix%3D%22lom%22%29%0A%7C+decode-xml%0A%7C+handle-generic-xml%28emitNamespace%3D%22true%22%2Cattributemarker%3D%22@%22%2Cvaluetagname%3D%22%C2%A7%22%29%0A%7C+encode-xml%28attributemarker%3D%22@%22%2Cvaluetag%3D%22%C2%A7%22%29%0A%7C+print%0A%3B%0A

This should be documented