title: how to include pdfpages in rmarkdown for beamer output
body: <p>I am creating pdf slides using rmarkdown and beamer.  When using latex instead of rmarkdown, I can include arbitrary pages from pdf files into my slides with</p>
  
  <pre><code>\usepackage{pdfpages}
  ...
  \includepdf[pages={1-10}]{another_file.pdf}
  </code></pre>
  
  <p>Is it possible to achieve this with rmarkdown?  Note that when just issuing the <code>\includepdf</code> command, intended to be located <em>between</em> slides, pandoc  wraps it between <code>\begin{frame}</code> and <code>\end{frame}</code>.</p>