* [DCG,DOC] Added README file.
* [DCG,DOC] Updated the documentation of the various modules.
* [DGRAPH,SC] Relocated DGRAPH modules into subdirectory.
* [GRAPH_THEORY,DOC] Added README file.
* [RDF_GRAPH,SC] Relocated RDF Graph modules into subdirectory.
* [UGRAPH,SC] Relocated UGRAPH modules into subdirectory.
* [DCG_CONTENT,NEW] Added horizontal_line//1.
* {DCG_CONTENT,EXT] The length of arrow//[1,2] now includes the pointing heads (if any).
* [COWSPEAK,DOC] Updated documentation's display of option lists.
* [GRAPH_EXPORT,FIX] remove_attribute/3 and shared_atrributes/2 were fixed.
* [GV_DCG,FIX] Default graph options need to be merged into the graph attributes (that are used in other locations as well).
* [GV_DCG,FIX] Corrected the indent of node and edge statements.
* [GV_DCG,FIX] The last code of quoted string content would not be written.
* [OPTION_EXT,NEW] Added option_dep/2 and subtract_option/3, supporting the deprecated option representation format.
* [RDF_EXPORT,FIX] Different versions of rdf_edge_arrow/2 and rdf_edge_style/2 would conflict.
* [RDF_GRAPH,FIX] One clause of rdf_term_name/3 was missing a cut.