Hashtags added to markdown parsing

htdocs/index.php

@@ -1047,6 +1047,12 @@ class Markdown {
 		$html = preg_replace('/~~(\S|\S.*?\S)~~/', '<strike>$1</strike>', $html);
 		// Code
 		$html = preg_replace('/`(\S|\S.*?\S)`/', '<code>$1</code>', $html);
+		// Hashtags
+		$html = preg_replace_callback('/(#[a-zA-Z][a-zA-Z0-9_]*)\b/', function($match) {
+			$hashtag = $match[1];
+			return '<a href="?search=' . urlencode($hashtag) . '">' .
+				htmlentities($hashtag) . '</a>';
+		}, $html);
 		return $html;
 	}