Merge tag '3.8.5' into develop

Release: 3.8.5
Preparation for new development cycle after release 3.8.5
Add CSS classes to output when on a single post
Add comment on the functionality.
Version bump 3.9.0-dev.4
Merge branch 'feature/issue_6' into develop

Closes #6
Update Changelog and add AUTHORS file
Update Spanish language
New language: Serbo-Croatian
Updated PO file
Update for translations
Version bump 3.9.0-rc.1
Version bump 3.9.0
Merge branch 'release/3.9.0'