Support collections

[peterdesmet]

Collections are a way to group content, see https://jekyllrb.com/docs/collections/

Parent page

• [x] Add a parent page pages/docs.md with permalink /docs/
• [x] Create new layout collection.html where collection items are listed
• [ ] Collection items could either be listed in a side menu (cf. Jekyll config) instead of toc or as cards ...
• [x] List collection items in navbar
• [x] Update config.yml
• [ ] Make sure collections only go one level deep? they won't

Collection pages

• [x] Make installation, configuration, markdown part of _docs collection
• [ ] Maybe add more dummy pages
• [x] Assign order attribute to pages
• [ ] Add category label to link back to collection page?? Maybe better if upward navigation is covered by breadcrumbs