isMarkdownFile = filepath => {
  if (!isFile2(filepath)) return false

  // Check symbolic link.
  if (isSymbolicLink(filepath)) {
    const targetPath = path.resolve(path.dirname(filepath), fs.readlinkSync(filepath))
    return isFile(targetPath) && hasMarkdownExtension(targetPath)
  }
  return hasMarkdownExtension(filepath)
}
Returns true if the path is a markdown file or symbolic link to a markdown file.

@param {string} filepath The path or link path.