Add support for comments to reader

[shaedrich]

Description

Since comments are part of the OOXML spec and I need to build an application that uses comments, I implemented them into phpWord

Fixes #1604 Fixes #622

Checklist:

• [ ] I have run composer run-script check --timeout=0 and no errors were reported
• [ ] The new code is covered by unit tests (check build/coverage for coverage report)
• [x] I have updated the documentation to describe the changes

[shaedrich]

I have run composer run-script check --timeout=0 and no errors were reported

I'm afraid, that list item is a little outdated since the version of php-cs-fixer is:

You are running PHP CS Fixer v2, which is not maintained anymore. Please update to v3. If you need help while solving warnings, ask at https://gitter.im/PHP-CS-Fixer, we will help you!

[shaedrich]

Can somebody help with this?

[Progi1984]

Superseeded by #2469