ox-html: Use OPTIONS items instead of keywords for booleans
* lisp/ox-html.el (html): Replace "HTML_HTML5_FANCY",
"HTML_INCLUDE_STYLE" and "HTML_INCLUDE_SCRIPTS" with, respectively,
":html5-fancy", "html-style" and "html-scripts" options.
(org-html-html5-fancy): Reformat docstring.
* doc/org.texi (HTML doctypes): Reflect keyword removal.
(CSS support): Reflect keyword removal.
The reasoning behind this change is that keywords can only store
strings as value. Therefore, they are not suited for toggles ("nil"
vs nil problem).