Clean up some code per @baweaver's suggestions.

lib/jekyll/renderer.rb

@@ -60,16 +60,14 @@ module Jekyll
     #
     # Returns the converted content.
     def convert(content)
-      output = content.dup
+      converters.reduce(content) do |output, converter|
-      converters.each do |converter|
         begin
-          output = converter.convert(output)
+          converter.convert output
         rescue => e
           Jekyll.logger.error "Conversion error:", "#{converter.class} encountered an error converting '#{document.relative_path}'."
           raise e
         end
       end
-      output
     end
 
     # Render the given content with the payload and info

lib/jekyll/site.rb

@@ -395,13 +395,13 @@ module Jekyll
     end
 
     def documents
-      docs = Set.new
+      collections.reduce(Set.new) do |docs, (label, coll)|
-      collections.each do |label, coll|
         if to_render.include?(label)
-          docs = docs.merge(coll.docs)
+          docs.merge(coll.docs)
+        else
+          docs
         end
       end
-      docs
     end
 
     def each_site_file