[Code Style] Changes in tag standards: Libraries/joomla

This pull should fix the issue detailed here: joomla/coding-standards#80

I have broken in parts this original pull #4590 to make it easy for review. This pull is contains only the libraries/joomla changes.
The components/, modules/, ... are going to be sent in different pulls.

This pull is related to #4603

Note for reviewer: I was going to break this into several pulls but I found easier to do it in different commints, so you can see the changes per commit at https://github.com/joomla/joomla-cms/pull/4617/commits.