title: YAML current date in rmarkdown
body: <p>I'm wondering if there's a trick to put the current date in the YAML front-matter of a <code>.rmd</code> document to be processed by <code>knitr</code> and the <code>rmarkdown</code> package. I used to have the following line at the top of my wiki pages,</p>
  
  <pre><code>   _baptiste, `r format(Sys.time(), "%d %B, %Y")`_
  </code></pre>
  
  <p>and it would get converted to <em>baptiste, 03 May, 2014</em> in the html output. Now, I would like to take advantage of the advanced pandoc wrapper provided by <code>rmarkdown</code>, but having r code in the YAML header doesn't seem to work:</p>
  
  <pre><code>---
  title: "Sample Document"
  output:
    html_document:
      toc: true
      theme: united
  date: `r format(Sys.time(), "%d %B, %Y")`
  author: baptiste
  ---
  
  Error in yaml::yaml.load(front_matter) : 
    Scanner error: while scanning for the next token at line 6, column 7
   found character that cannot start any token at line 6, column 7
  Calls: &lt;Anonymous&gt; ... output_format_from_yaml_front_matter -&gt; 
         parse_yaml_front_matter -&gt; &lt;Anonymous&gt; -&gt; .Call
  </code></pre>
  
  <p>Any workaround?</p>