The DBNL scrape now works for a few publications.

* [DBNL,EXT] Added support for indexed lines and unindexed lines and poem-like lines.
* [DBNL,EXT] Added support for page numbers.
* [DBNL,EXT] Skip spaces / empty contents.
* [DBNL,EXT] Added support for subheaders.
* [DBNL,EXT] Leave out paragraphs in cases where this only adds superfluous markup: around images and around empty content.
* [DBNL,EXT] Added support for (block)quotes.
* [DBNL,FIX] Several fixes during development.
* [LIST_EXT,NEW] Added split_list_exclusive/3.
* [RDF_DATATYPE,FIX] Added determinism for the XML Literal datatype.