title: How to output literal backticks in knitr::spin
body: <p>I'm trying to create some snippet templates for <code>knitr::spin</code> documents in R Studio, and I need them to include literal backticks so that the resulting document contains an R snippet:</p>
  
  <p>Example of desired output:</p>
  
  <pre><code>#' ---
  #' author: 'ENTER'
  #' title: 'ENTER'
  #' date: '`r Sys.time()`'
  #' output: 
  #'    html_document
  #' ---
  </code></pre>
  
  <p>However, I can't figure out how to output backticks.  This:</p>
  
  <pre><code>`r paste("#' date: '`Sys.time()`')`
  </code></pre>
  
  <p>will not work as the tick marks interrupt the paste command when rendering from R Studio snippet to R code. I've been trying to hash out the tick marks, adding forwards and backwards slashes etc., but haven't found a solution that renders this line correctly to:</p>
  
  <pre><code>#' date: '`r Sys.time()`'
  </code></pre>
  
  <hr>
  
  <p>Windows 7 Enterprise, 64-bit Operating System<br>
  R Version: 3.2.5<br>
  R Studio Version: 0.99.903<br>
  knitr Version: 1.14  </p>
  
  <hr>
  
  <p>Example: I tried this, but it still translates the R code instead of just printing the text:</p>
  
  <pre><code>snippet spin.header
  `r paste("#' ---")`
  `r paste("#' author: 'ENTER'")`
  `r paste("#' title: 'ENTER'")`
  `r paste("#' date:  '&lt;code&gt;``` `r Sys.time()` ```&lt;/code&gt;'")`
  `r paste("#' output:")` 
  `r paste("#'    html_document")`
  `r paste("#' ---")`
  </code></pre>