We look for .Params.featured_image
If found > we use that as URL
If we find a Page resource matching the value of the above, we use its .RelPermalink
If none of the above we look for an resource whose filepath contains `featured` or `cover` and use its .RelPermalink if found
Fixes#233Fixes#407
* Add support for auto-detection of featured images.
* Rename Partial, Add Documentation
Renamed the partial to func/GetFeaturedImage.html.
Additionally added more documentation in the partial to explain how it
worked, and what values were returned.
Co-authored-by: Sean Zimmermann <sz2243@columbia.edu>
