First beta version for Drupal 8.
New for Drupal 8 is that two different Markdown libraries can be used, and more may be added.
* PHP Markdown by Michel Fortin
* CommonMark
If you are comfortable with composer that is the best way to install both PHP Markdown and CommonMark. They will then be autoloaded just like other parts of Drupal 8.
The old way of installation in the libraries directory is only supported for PHP Markdown. The libraries module is then needed to load the library.