XL : 2.9.1 version to be compatible with new version of XTT 1.9.0

git-svn-id: https://plugins.svn.wordpress.org/xili-language/trunk@781348 b8457f37-d9ea-0310-8a92-e5e31aec5664
XL - add link in readme about new xtt

git-svn-id: https://plugins.svn.wordpress.org/xili-language/trunk@781354 b8457f37-d9ea-0310-8a92-e5e31aec5664