SilverStripe - ShowDown
Place these files in your silverstripe directory, in a directory called showdown/
Installing the module will by default provide a ShowdownPage type.
However, you may wish to simply override all HtmlTextFields with ShowdownTextField, in which case you may un-comment the line in _config.php. This will also override $Content in templates to display correctly.
To display fields other than Content correctly on the front-end, you will need to adjust the templates manually, as shown below:
Example of template display.
See also ShowdownPage.php