Many updates to modules: new modules for SCG and X11 colors, various GV variants, and various DCG variants.

* [BREWER,SC] Simplified existing code.
* [DCG_CARDINAL,EXT,SC] Relocated and adapted sign//0 and sign//1, coming from module DCG_ASCII.
* [DCG_CARDINAL,EXT] Changed the arguments for the digit DCG rules, now the decimal digit equivalent (used to be the code).
* [DCG_CARDINAL,NEW] Added decimal_number//1.
* [DCG_CONTENT,NEW] New module for often-used content DCGs, taken from DCG_GENERIC.
* [DCG_GENERIC,SC] Added dcg_end//0 to the public predicates.
* [DCG_GENERIC,EXT] Added dcg_call/4. Using meta-DCG rules now works (see dcg_multi_list//2).
* [DCG_GENERIC,EXT] dcg_peek//1 now also woks for nonvar DCG rule input (besides var code argument).
* [DCG_WRAP,SC] New module for wrapping of text. Contains line and word wrapping rules.
* [GRAPH_EXPORT,NEW] Added shared_attributes/3 which extracts the attributes that a given number of edge or vertex terms share. These shared attributes are then removed from each individual term. This allows (1) generic attributes to be asserted separately in GV, and (2) edge/vertex terms to be relatively short.
* [GV_ATTRS,SC] New module, taking the supported GV attributes from module GRAPHVIZ. All code was updated for the new situation.
* [GV_DCG,NEW] New module for the GV syntax implemented by DCG rules. The GV graph is parsed based on a given GIF argument (generation is too difficult).
* [GV_FILE,SC] New module, taking the GV file related predicates from module GRAPHVIZ.
* [GV_HASH,SC] New module, taken from module GRAPHVIZ.
* [RDF_SCRIPT,SC] Updated this module using the many improvements that were made in PGC.
* [SVG_COLORS,SC] New modules, taken from module SCG.
* [TYPECHECK,SC] Removed clauses that are already supported by swipl: boolean, oneof, double.
* [TYPECHECK,EXT] Extended must_be/2's behavior with open numeric intervals using between/2.
* [X11_COLORS,SC] New modules, taken from module X11.