We can now scrape quite some stuff from the DBNL. Some idiosyncratic pages still remain.

* [DBNL,FIX] Many fixes overall.
* [DBNL_DOWLOADS,FIX] Rewrote the downloads DCG. Now works.
* [DBNL_GENERIC,DB] Added some debug tools.
* [DBNL_GENERIC,SC] Added dbnl_save_image/[3,4], reducing code, increasing modularity.
* [DBNL_GENERIC,HACK] Extended the alterations dbnl_uri_resolve/3 should try in order to find the intended URI.
* [DBNL_GENERIC,DB] Added handlers for exceptions on http_open/3.
* [DBNL_MARKUP,EXT] Now parses rhet (/) SPAN class.
* [DBNL_MARKUP,EXT] Now parses special poetry headers (DTD extension).
* [DBNL_MARKUP,EXT] Now parses intertextual links.
* [DBNL_TEXT,FIX] The titlepage image in the right DIV was not crawled correctly.
* [DBNL_TEXT_LEFT,EXT] Now parses empty author.
* [DBNL_TEXT_LEFT,EXT] Gave up the parsing of sources. Now goes for the eay route: simple literals.
* [DBNL_LEFT_TEXT,EXT] Now parses the logo of a funder.