Added option to include html toc in ebook
Include in navigational toc only 'tocable' items
Fix formattin of TOC items whithout label
Merge branch 'master' into epubtoc

Conflicts:
	src/Easybook/Publishers/Epub2Publisher.php
Added test capability for EPUB files.
Added assertion for missing files in generated books.
Added test for HTML TOC generation in EPUB
Merge pull request #85 from magabriel/epubtoc

Added a new "use_html_toc" option to include an HTML "Table of Contents" in ebooks.

This commits make easybook ebooks compliant with Kindle Publishing Guidelines (http://kindlegen.s3.amazonaws.com/AmazonKindlePublishingGuidelines.pdf)