[Docs] Add some links in the services chapter

doc/services.rst

@@ -189,7 +189,7 @@ Silex defines a range of services.
   that is used internally. You can add, modify, read routes.
 
 * **controllers**: The ``Silex\ControllerCollection`` that is used internally.
-  Check the *Internals* chapter for more information.
+  Check the :doc:`Internals chapter <internals>` for more information.
 
 * **dispatcher**: The `EventDispatcher
   <http://api.symfony.com/master/Symfony/Component/EventDispatcher/EventDispatcher.html>`_
@@ -207,16 +207,16 @@ Silex defines a range of services.
   Request as input and returns a Response as output.
 
 * **request_context**: The request context is a simplified representation of
-  the request that is used by the Router and the UrlGenerator.
+  the request that is used by the Router and the :doc:`UrlGenerator </providers/url_generator.rst>`.
 
 * **exception_handler**: The Exception handler is the default handler that is
   used when you don't register one via the ``error()`` method or if your
   handler does not return a Response. Disable it with
   ``unset($app['exception_handler'])``.
 
-* **logger**: A ``Psr\Log\LoggerInterface`` instance. By default, logging is
+* **logger**: A `LoggerInterface <https://github.com/php-fig/log/blob/master/Psr/Log/LoggerInterface.php>`_ instance. By default, logging is
   disabled as the value is set to ``null``. To enable logging you can either use
-  the ``MonologServiceProvider`` or define your own ``logger`` service that
+  the :doc:`MonologServiceProvider <providers/monolog>` or define your own ``logger`` service that
   conforms to the PSR logger interface.
 
 .. note::