Ruleset extraction script: replaced call to die with a thrown exception.

Author: tomzx

scripts/extract-rules-from-ruleset.php

@@ -7,7 +7,7 @@
 if ($result) {
 	array_shift($matches);
 } else {
-	die('Cannot find rules in Ruleset.md');
+	throw new RuntimeException('Cannot find rules in Ruleset.md');
 }
 
 $rules = array_combine($matches['code'], $matches['level']);