Changed _plugins folder to plugins and updated rake tasks accordingly

.themes/classic/plugins/include_file.rb

@@ -0,0 +1,31 @@
+require 'pathname'
+
+module Jekyll
+
+  class IncludePartialTag < Liquid::Tag
+    def initialize(tag_name, file, tokens)
+      super
+      @file = file.strip
+    end
+
+    def render(context)
+      file_dir = (context.registers[:site].source || 'source')
+      file_path = Pathname.new(file_dir).expand_path
+      file = file_path + @file
+
+      unless file.file?
+        return "File #{file} could not be found"
+      end
+
+      Dir.chdir(file_path) do
+        partial = Liquid::Template.parse(file.read)
+        context.stack do
+          partial.render(context)
+        end
+      end
+    end
+  end
+end
+
+Liquid::Template.register_tag('include_partial', Jekyll::IncludePartialTag)
+