These changes are part of a big update to graph exporting, affecting all graph code.

* [CIRCULAR_GRAPH_REPRESENTATION,NEW] New module implementing circular coordinate generation.
* [DCG_HTML,NEW] Added dcg_style//1 for parsing the style attribute for HTML elements.
* [EXPORT_GRAPH_HTML,NEW] New module implementing the conversion from the Graph Intermediary Format to HTML.
* [GRAPH_EXPORT,SC] This module is slowly being removed. The code for exporting graphs is now in two types of files: (1) those that convert from a graph format to the Graph Intermediary Format, and (2) those that convert from the Graph Intermediary Format to some output format. We aim to include at least the following modules:
  (1.1) RDF -> GIF (1.2) UGraph -> GIF (1.3) DGraph -> GIF (2.1) GIF -> GV (2.2) GIF -> HTML (2.3) GIF -> SVG.
* [GRAPH_EXPORT_GRAPHVIZ,NEW] New module implementing the GIF to GZ conversion.
* [GRAPH_EXPORT_SVG,NEW] New module implementing the GIF to SVG conversion.
* [GRAPH_GENERIC,NEW] Big overhaul of all the code. These methods need to be generically applicable (i.e., independent of the graph format) in the new situation as well. We do this by including meta-predicates as parameters.
* [GRAPH_GENERIC,SC] Removed generic predicates that were merely wrappers around graph-specific functionality (e.g., edges1/2).
* [LIST_EXT,SC] Relocated nth0chk/3 and nth1chk/3, coming from MATH_EXT.
* [MARKUP,SC] Removed file_to_uri/2, use uri_file/2 from library uri instead.
* [PRINT_EXT,SC] Renamed formatnl/[1,2,3] to formatln/[1,2,3].
* [PRINT_EXT,NEW] Added print_nvpair/[1,2] for writing name-value pairs?
* [RDF_EXPORT,SC] Removed predicates that are no longer needed in the new GRAPH_EXPORT setup.
* [RDF_GRAPH,SC] Relocated rdf_triples_to_edges/2 and rdf_triples_to_vertices/2, coming from GRAPH_EXPORT?
* {RDF_GRAPH_THEORY,SC] Simplified predicates arguments, less options, graph argument, etc.
* [RDF_LIST,NEW] New module, moving RDF list related predicates from RDF_READ.
* [RDF_LIST,NEW] Added is_rdf_list/1 and rdf_list_member/2.
* [UGRAPH_EXPORT,NEW] Reworte the module to export to Graph Intermediary Format in the new situation.
* [UGRAPH_EXT,SC] Added library UGRAPHS to the public predicates using reexport/2 with predicate renamings.
* [UGRAPH_EXT,SC] Removed predicates that are also in GRAPH_GENERIC (e.g., component/2).
* [UGRAPH_EXT,NEW] Added is_ugraph/1.
* [UGRAPH_EXT,SC] Changes to predicate arguments: less options, separate graph argument, etc.