Add HTML5 tags and some cleanup

* package.lisp (:whopper): export def-html-tag
(:whopper-tags): import def-html-tag from :whopper: add HTML5
tags.
(:whopper-svg): Delete package.

* whopper.asd (:whopper): Add HTML5 tags

* whopper.lisp (%indent%): renamed from
%whopper-indentation-depth%.
(%code%): Renamed from %whopper-code%.

* tags/html5.lisp (href): Add HTML5 tags.

* tags/w3-tag-scraper.lisp (:whopper): Experimental scraping from
w3schoolds.com