Merge the Nook team's contribution to master

Markus and I met and talked and we had the same thought that instead of as originally planned make one final 3.x release before moving on to 4, we should consider doing this directly on 4, this motivated primarily by the massive delay of EpubCheck 3.x work we had over the spring. In other words, the plan would be: no
more 3.x releases at all.

The plan would be to:

 * resume work on the master branch for 4.x
 * support the following specs:
    * EPUB 3.0.1
    * EDUPUB Content Model
    * Indexes
    * Dictionaries
 * @mattgarrish is currently editing a document listing all the required updates, which will be ultimately converted to issues in the tracker (along with test cases when possible)
 * publish a beta release (or release candidate) by the end of August 

@santoch WDYT ? would you be working on master if this is merged, or keep on working on a separate branch ?