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>.