code: function replaceLinkWithEmbedded(node, index, parent, vFile) {
    const { title, url, position } = node;
    let newNode;
  
    // If the node isn't mermaid, ignore it.
    if (!isMermaid(title)) {
      return node;
    }
  
    try {
      const value = fs.readFileSync(`${vFile.dirname}/${url}`, { encoding: 'utf-8' });
  
      newNode = createMermaidDiv(value);
      parent.children.splice(index, 1, newNode);
      vFile.info('mermaid link replaced with div', position, PLUGIN_NAME);
    } catch (error) {
      vFile.message(error, position, PLUGIN_NAME);
      return node;
    }
  
    return node;
  }
docs: Given a link to a mermaid diagram, grab the contents from the link and put it
  into a div that Mermaid JS can act upon.
  
  @param  {object}   node
  @param  {integer}  index
  @param  {object}   parent
  @param  {vFile}    vFile
  @return {object}