Removed ids on elements that occur in a glossary so there is no chance for duplicate ids

A `cnx:definition` element that occurs in the `cnx:content` element was
being cloned (with ids) and inserted into the glossary causing the EPUB
generation to fail
Merge pull request #43 from Connexions/glossary-duplicate-ids

Removed ids on elements that occur in a glossary so there is no chance f...
Added documentation for removing glossary ids
Merge branch 'master' into regression-bugfixes