Merge pull request #83 from oreillymedia/htmlbook-xsl

Added $custom.chunk.wrapper param that lets you specify a custom chunk wrapper
Allow <img/> elements to be included in aside.
Merge pull request #85 from oreillymedia/xmlschema

Allow <img/> elements to be included in aside.
The "title" in the <head> is now the canonical location where the book title should be stored. Including an <h1> at the beginning of the <body> is now optional. htmlbook-xsl logic for EPUB updated accordingly, to look for title in <head> first and then in heading child of <body>.
Merge pull request #86 from oreillymedia/xmlschema

Updated book title requirements in XML Schema and corresponding XSL handling for EPUB
Let's turn .root.chunk off by default
Ensure <iframe> elements are not self-closing, as self-closing <iframe/> tags can cause rendering issues in browsers.