Add Xenus library (#666)

* Add Xenus to php-libraries.txt

Author: abellion

source/php-libraries.txt

@@ -37,6 +37,10 @@ Stand-alone Libraries
   **mongodb** extension. It is schema-less and supports fast object hydration
   and persistence, which makes it well-suited for modeling aggregation results.
 
+- `Xenus <https://github.com/abellion/xenus>`_ is an elegant MongoDB ODM
+  that supports events, relationships, embedded documents, and more.
+  It works on PHP 7+ and has an integration to the Laravel framework.
+
 Framework Integrations
 ~~~~~~~~~~~~~~~~~~~~~~
 
@@ -60,7 +64,11 @@ Framework Integrations
     library and includes an abstract model, a helper class for handling bulk
     writes, database wrappers for Laravel and Lumen, and some necessary helper
     functions.
-    
+
+  - `Xenus Laravel <https://github.com/abellion/xenus-laravel>`_ integrates
+    Xenus ODM with the Laravel and Lumen frameworks, adding failed jobs and
+    migrations capabilities.
+
 - Symfony
 
   - `MongoDB Bundle <https://github.com/facile-it/mongodb-bundle>`_: A