title: How can I access Middleman template helpers when extending a class in config.rb?
body: <p>This <code>config.rb</code> works:</p>
  
  <pre><code>helpers do
      def link_to_nothing(text)
          link_to(text, "#")
      end
  end
  </code></pre>
  
  <p>With template <code>index.html.erb</code>:</p>
  
  <pre><code>&lt;%= link_to_nothing "Test link" %&gt;
  </code></pre>
  
  <p><br>
  But when I try to add a method to the <code>Middleman::Sitemap::Resource</code> class in this <code>config.rb</code>:</p>
  
  <pre><code>helpers do
      class Middleman::Sitemap::Resource
          def link(text)
              link_to(text, path)
          end
      end
  end
  </code></pre>
  
  <p>With template <code>index.html.erb</code>:</p>
  
  <pre><code>&lt;%= current_page.link "This page" %&gt;
  </code></pre>
  
  <p>The following error comes up when loading the page:</p>
  
  <blockquote>
    <p>NoMethodError at /index.html</p>
    
    <p>undefined method `link_to' for #&lt;Middleman::Sitemap::Resource:0x3139848&gt;</p>
  </blockquote>