removed filename check in saveBook

It is really up to the calling function to ensure valid file names,
having the ePub classes do it in this case caused problems.

src/PHPePub/Core/EPub.php

@@ -2199,7 +2199,7 @@ function buildTOC($cssFileName = null, $tocCSSClass = "toc", $title = "Table of
     function saveBook($fileName, $baseDir = '.') {
 
         // Make fileName safe
-        $fileName = $this->sanitizeFileName($fileName);
+        // $fileName = $this->sanitizeFileName($fileName); // It is up to the user to ensure valid file names.
 
         // Finalize book, if it's not done already
         if (!$this->isFinalized) {