Merge pull request #76 from oreillymedia/xmlschema

Fixing some hrefs and ids in sample doc
Standard error reporting functionality.
Refactoring error handling.
Refactoring error handling.
Allow "terminate" value to be passed to log-message template as a parameter.
Handling for "DEBUG" level messages.
Refactored log/error handling for EPUB stylesheets.
Log/error handling refactoring for labeling.
Log/error handling refactoring for xrefgen.
Merge pull request #77 from oreillymedia/htmlbook-xsl

Standardized error handling
Modularized TOC title value generation to separate toc-title template.
Merge pull request #78 from oreillymedia/htmlbook-xsl

Modularized TOC heading value generation to create separate toc-title template.
Addded support for nesting <img> tags as children of <section> elements, as well as Part <div>s.