added popular exploration, added order:rank

app/controllers/explore/posts_controller.rb

@@ -0,0 +1,11 @@
+module Explore
+  class PostsController < ApplicationController
+    respond_to :html, :xml, :json
+    
+    def popular
+      @post_set = PostSets::Popular.new(params[:date], params[:scale])
+      @posts = @post_set.posts
+      respond_with(@posts)
+    end
+  end
+end