Support for new knitr option specification

[coatless]

Starting from {knitr} v1.35 onward, the options possible in an R Markdown file now include:

R inline style:

```{r}
#| echo = FALSE,
#| fig.width = 10
```

YAML style:

```{r}
#| echo: false
#| fig.width: 10
```

Any plans to support parsing these special comment options? #!

[joelnitta]

+1: It would be great to be able to convert between these two types of formats.

Doing so would help me solve this issue in a package I'm developing.