Add Multi Neighbors plugin.

.gitmodules

@@ -37,3 +37,6 @@
 [submodule "pelican-page-hierarchy"]
 	path = pelican-page-hierarchy
 	url = git://github.com/akhayyat/pelican-page-hierarchy
+[submodule "multi_neighbors"]
+	path = multi_neighbors
+	url = git@github.com:davidlesieur/multi_neighbors.git

multi_neighbors

@@ -0,0 +1 @@
+Subproject commit b6fcb4aed011a0b6bd90f19d7082e89b5aa481cf