title: will_paginate only show previous_page & next_page?
body: <p>I don't want to list out the number of each page. How can we just show "previous" and "next" with <code>will_paginate</code>?</p>
  
  <p><strong>view</strong></p>
  
  <pre><code>&lt;%= will_paginate @activities %&gt;
  &lt;% @activities.each do |activity| %&gt;
    etc...
  &lt;% end %&gt;
  </code></pre>
  
  <p><strong>controller</strong></p>
  
  <pre><code>class ActivitiesController &lt; ApplicationController
      def index
          @activities = Activity.order("created_at desc").where(user_id: current_user.following_ids).paginate(:page =&gt; params[:page])
      end
  end
  </code></pre>
  
  <p><strong>model</strong></p>
  
  <pre><code>class Activity &lt; ActiveRecord::Base
    self.per_page = 25
  
    def page_number
      (index / per_page.to_f).ceil
    end
  
    private
  
    def index
      Activity.order(created_at: :desc).index self
    end
  end
  </code></pre>