Create a code chunk in an RMarkdown document that is wider than the page and scrolls horizontally.

knitr_Wide_Output.Rmd

First-thing at the top of the Rmd file, after the YAML header, is the 
following css style block.

    <style>
    pre {
      overflow-x: auto;
    }
    pre code {
      word-wrap: normal;
      white-space: pre;
    }
    </style>

(Thanks to [this answer](https://stackoverflow.com/a/36846864/393354) by rawr on Stack Overflow.)

Alternatively, this css could be included in a css file that is 
included in the document via the YAML headers, like so:

    ---
    title: "Document Title"
    author: "John Author"
    date: '`r format(Sys.Date(), "%B %Y")`'
    output: 
      html_document: 
        css: custom_css.css
    ---

When we want to have a code chunk that scrolls, we use code blocks to 
save the current output width for R, then set a wide output width.

```{r, include=FALSE}
set_width <- getOption("width")
options(width = 999)
```

Then we produce our wide output, being sure to set the `tidy=FALSE`
chunk option.

```{r, tidy=FALSE}
mtcars %>% skim()
```

Finally, we set the output width back to the previous value so that
future code blocks will produce the normally-expected formatting.

```{r, include=FALSE}
options(width = set_width)
```