ability to define custom regex's for style placeholders

sometimes, developers like me want to redefine style placeholders
in their applications. From this patch, they can acchieve this from
simple get...Regex() method redefine.

src/Symfony/Component/Console/Output/Output.php

@@ -180,6 +180,26 @@ abstract class Output implements OutputInterface
      */
     abstract public function doWrite($message, $newline);
 
+    /**
+     * Gets regex for a style start.
+     *
+     * @return  string
+     */
+    protected function getStartStyleRegex()
+    {
+        return '#<([a-z][a-z0-9\-_=;]+)>#i';
+    }
+
+    /**
+     * Gets regex for a style end.
+     *
+     * @return  string
+     */
+    protected function getEndStyleRegex()
+    {
+        return '#</([a-z][a-z0-9\-_]*)?>#i';
+    }
+
     /**
      * Formats a message according to the given styles.
      *
@@ -189,9 +209,9 @@ abstract class Output implements OutputInterface
      */
     protected function format($message)
     {
-        $message = preg_replace_callback('#<([a-z][a-z0-9\-_=;]+)>#i', array($this, 'replaceStartStyle'), $message);
+        $message = preg_replace_callback($this->getStartStyleRegex(), array($this, 'replaceStartStyle'), $message);
 
-        return preg_replace_callback('#</([a-z][a-z0-9\-_]*)?>#i', array($this, 'replaceEndStyle'), $message);
+        return preg_replace_callback($this->getEndStyleRegex(), array($this, 'replaceEndStyle'), $message);
     }
 
     /**