Various small updates to the RDF and RFC modules.
Testing of `rdf_term_name`.
The new DCG for GV now writes a somewhat valid DOT file!

* [DCG_CARDINAL,EXT] Added arguments for codes and numbers.
* [DCG_CARDINAL,FIX] Rewrote [un]signed_number//2.
* [DCG_CONTENT,FIX] Added setting idnent_size/1.
* [DCG_GENERIC,FIX] There were problems with an uninstantiated `:DCGBody` argument. Simplified dcg_peek//1 (revert).
* [GV_ATTRS,EXT] Added support for the deprecated option representation format.
* [GV_DCG,EXT] The new DCG for GV is able to output almost valid DOT files based on GIF input.
* [MATH_EXT,NEW] Added number_length/2.