adding HTML5 elements, from Text.Blaze.Html5

Grabbed list of HTML5 elements from Text.Blaze.Html5 (https://github.com/jaspervdj/blaze-html/blob/master/src/Util/GenerateHtmlCombinators.hs). This should probably be generated (like Blaze) in the future - but this will at least get folks up-and-running!

Note that there is a valid STYLE tag in HTML4 and HTML5 - yet the top-level "style" function is used for attribute-setting.