document genres methods

NetBiblio.php

@@ -490,17 +490,31 @@ class NetBiblio extends WebService
         return AudioBook::listOfReaders();
     }
 
+    /**
+     * This method is called by the website in Drupal to get the list
+     * of available 'Genres'.
+     * @return array
+     */
     public function ListOfGenres()
     {
         return AudioBook::ListOfGenres();
     }
 
+    /**
+     * This method is called by the Android application to get the list
+     * of available 'Genres'.
+     * @return array
+     */
     public function ListOfCategories()
     {
-        // this method exists for compatibility purpose with the Android and iOS applications
-        return $this->ListOfGenres();
+        return AudioBook::ListOfGenres();
     }
 
+    /**
+     * This method is called by the iOS application to get the list
+     * of available 'Genres'. 'Jeunesse' must be a part of them.
+     * @return array
+     */
     public function ListOfTypes()
     {
         return array_map(function($g) {