* [DCG_GENERIC,SC] Renamed dcg_stream/2 to dcg_with_output_to/2, in order to indicate its broader applicability.
Cleanup of all DCG-based HTML code.

* [HTML_DCG,SC] New module collecting DCG rules for HTML expressions from modules DCH_HTML (now phased out) and HTML.
* [HTML_DCG,SC] Renamed html_entity//[1,2] to html_element//[1,2].
* [HTML_DCG,NEW] Added html_entity//[0,1].