Changed format to follow EPUB3 navigation format
Changed classes for ToC links

to make it clear when a title should be autogenerated from the module
and when it is overridden
Ensure math elements belong to the MathML namespace
Added support for additional figure/table attributes
Convert label element to data-label attribute
Intramodule links only rely on the href
Merge pull request #7 from Connexions/generate-epub-nav-toc

Changed format to follow EPUB3 navigation format