Add columns parameter (#308)

This doesn't do anything now, but will be need for the theme release.

Author: jarrodmillman

core-projects/_index.md

@@ -28,7 +28,7 @@ as other community members (e.g., contributors to other ecosystem projects).
 
 ### Core Projects
 
-{{< page_gallery pages="." link=internal >}}
+{{< page_gallery pages="." link=internal columns="2 3 4 5" >}}
 
 ## Implementation