Support Markdown syntax in P2 posts and comments

functions.php

<?php

// http://michelf.com/projects/php-markdown/extra/
require_once( dirname(__FILE__) . '/markdown-extra/markdown-extra.php' );

/**
 * Format posts/comments with Markdown at display time. Only process
 * blocks starting with \^md\s+.
 **/
function p2mis_comment_markdown( $text ) {
	if( ! function_exists('Markdown') ) {
		return $text;
	}

	if( preg_match( '/^\^md\s+/i', $text ) ) {
		$text = preg_replace( '/^\^md\s+/i', '', $text );
		$text = Markdown($text);
	}

	return $text;
}
add_filter( 'comment_text', 'p2mis_comment_markdown', 1 );
add_filter( 'the_content', 'p2mis_comment_markdown', 1 );

// Remove the P2 list processing, which converts lists to HTML on save
add_filter( 'p2_add_component_post-list-creator', '__return_false' );
add_filter( 'p2_add_component_comment-list-creator', '__return_false' );