* Add initial breadcrumb partial
* Add aria-current=page property
* Add separators via CSS to be comply with screen readers
* Use ordered list to the set of links
* Update README.md: add breadcrumb section
WARNING: UPGRADE HUGO TO VERSION 0.54.0 OR LATER
* post_thumbnail -> post_featured
* Add url, alt, caption and credit params for featured
* Add previewOnly param
* Add styles for featured
* Add fallback for thumbnail.*
* Add "Featured Images" page
* Show caption & credit on single pages only
* Update README: add featured image guide
* Bump Hugo min version because `reflect.IsMap` [0.38 -> 0.54.0]