Convert a Jekyll-based lesson to a sandpaper-based lesson

Usage

use_sandpaper(body, rmd = TRUE, yml = list(), path = NULL, known_paths = NULL)

body: the xml body of an episode
rmd: if TRUE, the chunks will be converted to RMarkdown chunks
yml: a list derived from the _config.yml file that defines the site variables.
path: the path to the source of the body. Defaults to NULL. This is used in conjunction with known_paths
known_paths: a character vector with the known paths in the lesson. This is used to determine the correct path to other files in the lesson.

the body

A Jekyll episode is littered with kramdown inline attribute tags and liquid-formatted links. Converting to sandpaper means the following:

links using liquid formatting (e.g. [text]({{ site.path }}/01-episode/) are replaced with their relative counterparts ([text](01-episode.md).
include statements for links.md and base_path.md are removed
image attributes have the kramdown : removed
code blocks with a kramdown inline attribute tag are converted to commonmark via the internal liquid_to_commonmark().
Lesson template-specific code is removed from the setup chunk in R Markdown files.