title: :footnotes extension won't work in Redcarpet Ruby gem
body: <p>I must be missing something very obvious -- I can't get footnotes to work with redcarpet. I have version 3.0.0:</p>
  
  <pre><code>&gt; gem list redcarpet
  *** LOCAL GEMS ***
  
  redcarpet (3.0.0)
  </code></pre>
  
  <p>I am trying code from the <a href="https://github.com/vmg/redcarpet/blob/59bfded76b99700c0c34a2a0fda29cffc46ec242/test/html_render_test.rb" rel="nofollow">test code on the Github repo</a> that has footnotes and it won't convert the Markdown to HTML that contains the footnote. I reduced the code down to just the footnotes function and <a href="https://gist.github.com/siruguri/6603806" rel="nofollow">put it on Gist</a>.</p>
  
  <p>The output is simply as follows:</p>
  
  <pre><code>&lt;p&gt;This is a footnote.[^1]&lt;/p&gt;
  &lt;p&gt;[^1]: It provides additional information.&lt;/p&gt;
  </code></pre>
  
  <p>What am I missing here?</p>