Very big cleanup operation mostly focussing on writing terms and generating HTML.

* [DCG_COLLECTION,SC] Functionality-preserving complete rewrite of all predicates:
  ** Extracted meta-options as meta-arguments.
  ** Removal of options arguments.
  ** Simplified code overall.
* [DCG_CONTENT,NEW] Added transition//2 and indent//2.
* [DCG_CONTENT,SC] Removed unused word//2 (no parse tree needed for this constituent).
* [DCG_GENERIC,NEW] Added dcg_with_output_to/2.
* [DCG_PROOF,SC] Proof printing in separate module.
* [DCG_STREAM,SC] Removed this module, obsoleted by dch_with_output_to/2 in DCG_GENERIC.
* [HTML_DROPDOWN_LIST,NEW] New module for generating dropdown lists in HTML.
* [HTML_TABLE,SC] Functionality-preserving complete rewrite, leaving only the DCG-based approach.
* [RDF_ENT,RDFS_ENT,RDF_MAT,NEW] Added regime/1 multifile.
* [RDF_HTML,RDF_HTML_TABLE,RDF_HTML_TERM,SC] Split into two modules.
* [RDF_MAT_WEB,RDF_WEB,SC] Split Web interface for RDF materialization into a separate module.
* [RDF_TABLE,RDF_TABULAR,SC] Simplification of codebase by using rdf_html_table//2 i.o. html_table//4.
* [RDF_DCG,RDF_NAME,SC] Functionality-preserving complete rewrite of all RDF term-writing predicates.
  ** Replaced all format-based predicates with DCG-based ones.
  ** Vastly reduced the number of public predicates / easier API.
* [RDF_LIST,SC] Code simplification due to SWI7's treatment of `[]` (as non-atom).
* [RDF_PARSE,NEW] New module for parsing RDF terms, taken from the old RDF_DCG.
* [RDF_REIFICATION,SC] Functionality-preserving merging of format-based and DCG-based methods for writing RDF statements (now DCG-only). Vastly simplifying codebase.
* [TMS_WEB,SC] Big cleanup.
* [WEB_MESSAGE,SC] Big cleanup.
* [WEB_UI,NEW] Added dom_as_atom//1 for including non-DCG accessible DOM parts in a generated Web page.