Merge pull request #94 from oreillymedia/htmlbook-xsl

Refinements to cover handling
Turning off $html4.structural.elements by default in epub.xsl
Modifying main h:nav template so it can be used as a named template as well.
Go ahead and allow TOC generation for every <nav data-type="toc"> in the content? (Do not really see a compelling argument to restrict to just the first <nav>)
Adding $scope param for specifying the scope at which a TOC will be generated (from root, from Chapter, etc.)
Support for TOC generation in process-chunk-wrapper mode.
Merge pull request #95 from oreillymedia/chunk-wrapper

Refined TOC generation handling and support for TOC generation in chunk-wrapper mode
Turn off generation of border <div>s for figures by default.