Include original markdown files in build output.

_plugins/markdown_and_sign.rb

@@ -0,0 +1,11 @@
+# Copy all of the source markdown files directly into the destination.
+Jekyll::Hooks.register :site, :post_write do |site|
+  dest = site.dest
+  categories = site.config['category_metadata'].each_key do |category|
+    dir = Dir.new("#{site.source}/_posts/#{category}")
+    dir.each do |filename|
+      next unless filename =~ /\.md$/
+      FileUtils.cp("#{dir.path}/#{filename}", "#{dest}/#{category}/")
+    end
+  end
+end