Function write_refdefs_to 

pub fn write_refdefs_to<P1, P2>(
    src_dir_path: P1,
    dest_file_path: P2,
) -> Result<()>
where
    P1: AsRef<Path>,
    P2: AsRef<Path>,

Parse Markdown from all .md files in a given source directory and write reference definitions found therein to a file.

src_dir_path: path to the source directory.

dest_file_path: path to the file to create and write into.