Spec updates for new header content model.
Merge pull request #126 from oreillymedia/schema

Updated specifications for subtitle handling
Handling for print URLs in parens for xrefgen.xsl
Handling for print URLs in chunk.xsl
Adding parameterized support for admonition headings.
Proper gentext handling for XREFs to sidebars.
Refactor handling for html4.structural elements (when enabled) to duplicate HTML5 structural semantic block elements as <div>s and move IDs to those <div>s to ensure better compatibility with EPUB 2-only ereaders.
Fixed url.in.parens handling for "stealth" XREFs; <a> elements with "XREF" hrefs but no corresponding data-type declaration.
Merge pull request #129 from oreillymedia/urls

Print URLs, admonition headings, EPUB 2 compatibility, and sidebar XREFs
No <div class="border-box"> for figures that have an empty <figcaption>
Merge pull request #130 from oreillymedia/figs

Fix for figure.border.div handling
Fix for empty figcaptions that works properly in both saxon and xsltproc.
Merge pull request #131 from oreillymedia/figs

Take 2 on Fix for figure.border.div handling
Refactored figure.border.div handling.
Merge pull request #132 from oreillymedia/figs

Refactored figure.border.div handling
Merge commit '73534ced7662218844977392dce46eb84cce21b4'

* commit '73534ced7662218844977392dce46eb84cce21b4':
  Refactored figure.border.div handling.
  Fix for empty figcaptions that works properly in both saxon and xsltproc.
  No <div class="border-box"> for figures that have an empty <figcaption>
  Fixed url.in.parens handling for "stealth" XREFs; <a> elements with "XREF" hrefs but no corresponding data-type declaration.
  Refactor handling for html4.structural elements (when enabled) to duplicate HTML5 structural semantic block elements as <div>s and move IDs to those <div>s to ensure better compatibility with EPUB 2-only ereaders.
  Proper gentext handling for XREFs to sidebars.
  Adding parameterized support for admonition headings.
  Handling for print URLs in chunk.xsl
  Handling for print URLs in parens for xrefgen.xsl
  Spec updates for new header content model.

Conflicts:
	index.html