Just a quick announcement to say I've update the Markdown editor plugin! It uses the latest "PageDown" version for the client-side editor, and I switched to a different PHP Markdown parser (cebe/markdown) which is much faster and uses better PHP code. Requires PHP 5.4.
It's also possible to extend it yourself if you so wanted by adding functions to the MyMarkdown.php class (see the cebe/markdown repo for details on how extending works)
Answer below if you find any problems.