Added some debugging tools for RDF.

* [DEB_EXT,SC] Removed RDF-related predicates.
* [HTML,FIX] list_to_table/3 would not work for markup inside table cells.
* [RDF_DEB,DEB] New module for debug tools for RDF data.
** Contains rdf_graphs_web/1 giving an HTML table overview of RDF graphs.
* [HTML_TABLE,SC] New module for generating HTML tables.
* [HTML_TABLE,EXT] Added option for row indexing.
* [META_EXT,NEW] Added boolean/2.
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