Several small fixes.

* [FILE_EXT,FIX] Added determinism to file_type_alternative/2.
* [RDF_BUILD,FIX] Added explicit XML namespace registration statement.
* [RDF_DATATYPE,FIX] Added explicit XML namespace registration statement.
* [RDF_EXPORT,FIX,SC] Added explicit XML namespace registration statement. Removed superfluous XML namespace registration statements.
* [RDF_GRAPH_THEORY,FIX] Missing argument corrected in rdf_edge/2.
* [RFC,SC] Collected all RFC module meta-data statements into this module. Use RDF_BUILD and RDFS_BUILD.
* [GRAPH_EXPORT,DOC] Updated the documentation for the graph export options.
* [PRINT_EXT,NEW] Added print_list/3 and print_set/3 that allow options to be set on list and set writing.
* [RDF_GRAPH,EXT] Rewrote parts of rdf_term_name/3:
** Better serialization for lists and sets (no begin/end char, newline separators).
** Improvements for typed literals (datatype is named too).
** New options for setting the way in which URIs are named.
Major overhaul of the options for RDF export.

* [GRAPH_EXPORT,DOC] Updated the documented options for graph_export/[3,4].
* [RDF_EXPORT,DOC] Updated the documented options for export_rdf_graph/[3,4] and rdf_rdge_name/3.
* [RDF_EXPORT,FIX] Fixed the use of replacements in RDF edge naming.
* [RDF_EXPORT,FIX] Fixed the assignment of styles to special RDF properties.
* [RDF_GRAPH_THEORY,SC] Removed double checking of the literals/1 option: already done in rdf_vertex/[2,3], so no need to do this in rdf_edge/[2,3] as well.
* [RDF_GRAPH_THEORY,SC] Removed the directed/1 option from rdf_edge/[2,3].
* [RDF_GRAPH_THEORY,SC] Removed the named_edges/1 option from rdf_edge/[2,3] and rdf_vertex/[2,3]. This is done in module RDF_EXPORT (when creating the edge term).
* [RDF_GRAPH_THEORY,SC] Removedd the vertex/1 option from rdf_vertex/[2,3].
* [RDF_GRAPH_THEORY,EXT] Rewrote the support for options literals/1 and rdf_list/1 for rdf_vertex/[2,3].
Various fixes for exporting RDF graphs to GV.

* [PRINT_EXT,FIX] print_list/3 would use a wrong opening bracket char.
* [RDF_EXPORT,FIX] Do not include vertices that do not occur in an edge (i.e., only predicate occurrences).
* [RDF_EXPORT,FIX] rdf_edge_arrow_head/2 was broken.
* [RDF_EXPORT,FIX] rdf_edge_style/2 would not use dynamic assertions.
* [RDF_GRAPH_THEORY,FIX] Faulty option handling in rdf_vertex_check/2.
* [RDFS_READ,EXT] rdfs_preferred_label/3 now accepts non-atomic arguments for the label parameter.
* [UGRAPH_EXPORT,RDF_EXPORT,FIX] Option arrow_type/1 renamed to arrowhead/1.