To use:
1. Set `list_format = 2` in `content/home/posts.md`
2. Refactor a post named `X.md` to `content/post/X/index.md`
3. Add an image named `featured.*` to your post's new folder
* feature is consistent across Posts, Projects, Talks, Publications, and nodes (#105)
* `image` parameter is moved under a `[header]` section at the end of existing content's frontmatter
* `caption` parameter can be used to specify image credit/caption (#103)
* set `preview = false` under `[header]` to hide a post's thumbnail on homepage (#113)
* add example of customizing a taxonomy list page at `/tags/academic/`
* revert i18n->hard-coded change for node page titles (#118)
George Cushen