title: Add properties to a page from a Jekyll plugin
body: <p>Say I want to have a page with content like this:</p>
  
  <pre><code>&lt;h1&gt;{{page.comment_count}} Comment(s)&lt;/h1&gt;
  {% for c in page.comment_list %}
  &lt;div&gt;
      &lt;strong&gt;{{c.title}}&lt;/strong&gt;&lt;br/&gt;
      {{c.content}}
  &lt;/div&gt;
  {% endfor %}
  </code></pre>
  
  <p>There are no variables on the page named <code>comment_count</code> or <code>comment_list</code> by default; instead I want these variables to be added to the page from a Jekyll plugin. Where is a safe place I can populate those fields from without interfering with Jekyll's existing code?</p>
  
  <p>Or is there a better way of achieving a list of comments like this?</p>