implementation of the HTML5 Outline algorithm

 Resource Description Framework (RDF) is a standard model
 for data interchange on the Web.
 .
 HTML::HTML5::Outline is an implementation
 of the HTML5 Outline algorithm,
 as per http://www.w3.org/TR/html5/sections.html#outlines .
 .
 The module can output a JSON-friendly hashref, or an RDF model.