Transform a path for passing to pandoc on the command line. Calls
path.expand on all platforms. On Windows,
transform it to a short path name if it contains spaces, and then convert
forward slashes to back slashes (as required by pandoc for some path
pandoc_path_arg(path, backslash = TRUE)
Path to transform
Whether to replace forward slashes in
backslashes on Windows.
Transformed path that can be passed to pandoc on the command line.