add ContributorsFromGit dzil plugin

This will add the list of contributors to the project -- as divined from the
authors of the reachable commits -- to the x_contributors metadata tag.  Other
tools and sites, like http://metacpan.org use this information to list
contributors.

dist.ini

@@ -31,3 +31,4 @@ folder = eg
 [PruneFiles]
 filenames = FacebookGraph.kpf
 
+[ContributorsFromGit]