Introducing a new API for downloading-extracting-loading (RDF) files from URLs.

* [ARCHIVE_EXT,FIX] Wrapper wrong instantiation.
* [DBPEDIA_CATEGORIES,SC] Tried out the new API for downloading, extracting, and loading files. Fastly reducing and simplifying code.
* [RDF_SERIAL,NEW] Added rdf_download_extract_load/2.
* [URI_EXT,NEW] Added download_and_extract_to_files/3.
* [URI_EXT,EXT] url_to_file_name/2 no longer builds the directory. Also updates to download_to_file/3 because of this.