Add "<- Previous" and "Next ->" buttons to blog posts

It's a very common practice, and we miss this in our blog.

Here's something to try:

   <ul class="high">
      <li>
        <% prev_article = current_article.previous_article %>
          <% if prev_article %>
          <a href="<%= prev_article.url %>" rel="prev" title="Previous article: <%= prev_article.title %>"> <%= prev_article.title %> </a>
          <% end %>
      </li>
      <li>
        <% next_article = current_article.next_article %>
          <% if next_article %>
          <a href="<%= next_article.url %>" rel="next" title="Next article: <%= next_article.title %>"> <%= next_article.title %> </a>
          <% end %>
      </li>
    </ul>

cc/ @regisF