DBNL is somewhat usable again after the big cleanup into modules.

* [DBNL_DB,NEW] Added dbnl_assert_copyright/4 and dbnl_assert_organization/3.
* [DBNL_EXTRACT,NEW] Added extract_copyright/3.
* [DBNL_GENERIC,SC] Rewote most of the XPath based crawling predicates to use a modular style.
* [DBNL_INDEX,FIX] Fixed dbnl_index_title/[2,3] which needs to first create a title resource, and can then add properties to it.
* [DBNL_TEXT,EXT] Greatly extended the HTML content that is explicitly parsed:
** Title.
** Author (empty and non-empty).
** Subordinate title (empty).
** Empty paragraphs.
** Notes mentioning the availability of only scans.
** Linebreaks.
** Copyright atoms (see DBNL_EXTRACT and DBNL_DB).
* [HTML,EXT] Some changes to the options for stream_to_html/2.