Merge branch '2.3' into 2.7

* 2.3:
  Updated all the README files
  [TwigBundle] Fix failing test on appveyor
  [FrameworkBundle] Fix a regression in handling absolute and namespaced template paths
  Allow to normalize \Traversable
  Remove _path from query parameters when fragment is a subrequest and request attributes are already set Added tests for _path removal in FragmentListener
  Simplified everything
  Added a test
  Fixed the problem in an easier way
  Fixed a syntax issue
  Improved the error message when a template is not found
  [CodingStandards] Conformed to coding standards
  [TwigBundle] fixed Include file locations in "Template could not be found" exception

Author: fabpot

README.md

@@ -1,42 +1,13 @@
 Debug Component
 ===============
 
-Debug provides tools to make debugging easier.
-
-Enabling all debug tools is as easy as calling the `enable()` method on the
-main `Debug` class:
-
-```php
-use Symfony\Component\Debug\Debug;
-
-Debug::enable();
-```
-
-You can also use the tools individually:
-
-```php
-use Symfony\Component\Debug\DebugClassLoader;
-use Symfony\Component\Debug\ErrorHandler;
-use Symfony\Component\Debug\ExceptionHandler;
-
-if ('cli' !== php_sapi_name()) {
-    ini_set('display_errors', 0);
-    ExceptionHandler::register();
-} elseif (!ini_get('log_errors') || ini_get('error_log')) {
-    ini_set('display_errors', 1);
-}
-ErrorHandler::register();
-DebugClassLoader::enable();
-```
-
-This component can optionally take advantage of the features of the HttpKernel
-and HttpFoundation components.
+The Debug component provides tools to ease debugging PHP code.
 
 Resources
 ---------
 
-You can run the unit tests with the following command:
-
-    $ cd path/to/Symfony/Component/Debug/
-    $ composer install
-    $ phpunit
+  * [Documentation](https://symfony.com/doc/current/components/debug/index.html)
+  * [Contributing](https://symfony.com/doc/current/contributing/index.html)
+  * [Report issues](https://github.com/symfony/symfony/issues) and
+    [send Pull Requests](https://github.com/symfony/symfony/pulls)
+    in the [main Symfony repository](https://github.com/symfony/symfony)