title: Adding a line break to code blocks in R Markdown
body: <p>I am using the knitr package with R Markdown to create an HTML report. I am having some trouble keeping my code on separate lines when using '+'.</p>
  
  <p>For example,</p>
  
  <pre><code>```{r}
  ggplot2(mydata, aes(x, y)) +
     geom_point()
  ```
  </code></pre>
  
  <p>will return the following the the HTML document</p>
  
  <pre><code>ggplot2(mydata, aes(x, y)) + geom_point()
  </code></pre>
  
  <p>Normally this is fine, but the problem arises once I start adding additional lines, which I want to keep separate to make the code easier to follow. Running the following:</p>
  
  <pre><code>```{r}
  ggplot2(mydata, aes(x, y)) +
     geom_point() +
     geom_line() +
     opts(panel.background = theme_rect(fill = "lightsteelblue2"),
          panel.border = theme_rect(col = "grey"),
          panel.grid.major = theme_line(col = "grey90"),
          axis.ticks = theme_blank(),
          axis.text.x  = theme_text (size = 14, vjust = 0),
          axis.text.y  = theme_text (size = 14, hjust = 1.3))
  ```
  </code></pre>
  
  <p>Will result in all the code coming out in one line, making it harder to follow:</p>
  
  <pre><code>ggplot2(mydata, aes(x, y)) + geom_point() + geom_line() + opts(panel.background = theme_rect(fill = "lightsteelblue2"), panel.border = theme_rect(col = "grey"), panel.grid.major = theme_line(col = "grey90"), axis.ticks = theme_blank(), axis.text.x  = theme_text (size = 14, vjust = 0), axis.text.y  = theme_text (size = 14, hjust = 1.3))
  </code></pre>
  
  <p>Any help in solving this would be greatly appreciated!</p>