feat: Allows commas to be included in tel URI (#389)

* Allows commas in tel URI scheme validator (addresses #388)

* Adds comment explaining 8429f7b

library/HTMLPurifier/URIScheme/tel.php

@@ -33,9 +33,9 @@ public function doValidate(&$uri, $config, $context)
         $uri->host     = null;
         $uri->port     = null;
 
-        // Delete all non-numeric characters, non-x characters
+        // Delete all non-numeric characters, commas, and non-x characters
         // from phone number, EXCEPT for a leading plus sign.
-        $uri->path = preg_replace('/(?!^\+)[^\dx]/', '',
+        $uri->path = preg_replace('/(?!^\+)[^\dx,]/', '',
                      // Normalize e(x)tension to lower-case
                      str_replace('X', 'x', rawurldecode($uri->path)));