Updated params to OPDS search endpoint
* [https://library.kiwix.org/catalog/searchdescription.xml https://library.kiwix.org/searchdescription.xml] which proposes an overall OPDS description in XML format
* http://library.kiwix.org/catalog/search which accepts a few GET parameter:
** <code>q=<PATTERN></code> which proposes a keyword based search in the catalogue
** <code>lang=fra</code> which proposes a language filter. Use an ISO639-3 language value (like in ZIM metadata).
* http://library.kiwix.org/catalog/root.xml which proposed the index of all the books