code: function getContentFromNode(options, node) {
  	return new Promise(function (resolve, reject) {
  		if (node.tag === 'link') {
  			return fs.readFile(normalizePath(node.attrs.href, options.root, options.from), 'utf8', function (err, res) {
  				return err ? reject(err) : resolve(res);
  			});
  		}
  
  		return resolve(node.content);
  	});
  }
docs: retieves content of node element
  or reads file from href attribute of <link module>
  @param  {Object} node
  @return {Promise<String>} contents of file or <style> tag