doc outline, schematron, data-* to class, h1-h6, element fixes

* line changed from span to p
* fixed linenum (should be span, not @value)
* data-showin changed to classes
* data-render changed to classes
* data-type changed to classes
* added document structure (cover,frontmatter,bodymatter,backmatter, and their children)
* doctitle moved to titlepage
* covertitle moved to cover (jacketcopy)
* using schematron to validate classes and epub:types
* fixed pagebreaks; @title used instead of content to describe page number
* now using all h1-h6 levels instead of only h1