Problem: how stale is the extension version?

Solution: include `#release_date` information when feasible

For git-based repos, this is the date of the top commit in the checkout.

Author: yrashk

lib/pgpm/package/git.rb

@@ -74,6 +74,10 @@ def source
         end
       end
 
+      def release_date
+        ::Git.open(source).log.first.date
+      end
+
       def self.included(base_class)
         base_class.extend(ClassMethods)
       end

lib/pgpm/package/metadata.rb

@@ -19,6 +19,8 @@ def license
         "TODO: license"
       end
 
+      def release_date; end
+
       def broken?
         requires.any?(&:broken?)
       end