Make cnxauthoring.Resource a subclass of cnxepub.Resource
Refactor initialize metadata and to_dict code
Subclass cnxepub.Document and cnxepub.Binder
Merge pull request #38 from Connexions/use-cnxepub-models

Use cnxepub models
Return 401 Unauthorized instead of 403 Forbidden if user is not logged in
Merge pull request #36 from Connexions/return-401

Return 401 Unauthorized instead of 403 Forbidden if user is not logged in