w3c-footnote custom element

Extends the HTML footer (http://www.w3.org/html/wg/drafts/html/master/sections.html#the-footer-element) element to identify its use for footnotes. Adds sub-role label text (offscreen) and icon via CSS. adds ARIA role=note

demo: http://thepaciellogroup.github.io/w3c-footnote/

The intent of this custom element is to provide a semantic identifier for footnote content, which does not currently have a dedicated element in HTML [1]

The footer element is used as an extension point as it is recommended to be used a container element for footnotes in HTML blockquotes [2]

[1] http://www.w3.org/html/wg/drafts/html/master/common-idioms.html#footnotes
[2] http://www.w3.org/html/wg/drafts/html/master/grouping-content.html#the-blockquote-element