Attr complete

New source ac-source-html-attribute-value and populated data for it in html-stuff/html-attributes-complete/

My data generator tool located https://github.com/osv/h5doc (see text/attrib.yaml). Lot of hand work from w3scool and http://www.w3.org/TR/html5 done, so it almost complete and quick-help also available for complete's values. But if you have some notice about attribute values, please let me know, I update h5doc and make for you fresh html-attributes-complete.

Also added to readme little hint about customization.