Make tag registry enumerable

lib/liquid/template.rb

@@ -19,6 +19,8 @@ module Liquid
     @@file_system = BlankFileSystem.new
 
     class TagRegistry
+      include Enumerable
+
       def initialize
         @tags = {}
         @cache = {}
@@ -41,6 +43,10 @@ module Liquid
         @cache.delete(tag_name)
       end
 
+      def each(&block)
+        @tags.each(&block)
+      end
+
       private
 
       def lookup_class(name)