bug #389 Made the slugger compatible with every language (javiereguiluz)

This PR was squashed before being merged into the master branch (closes #389).

Discussion
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Made the slugger compatible with every language

In the Symfony Installer we recently made a change to forbid any non-Latin character in the project names ([see details](symfony/symfony-installer#278)). This is needed because Composer itself requires that for package names.

In the Symfony Demo app we had a similar problem with the slugs of the blog posts. We removed any non-Latin character ... but that caused bugs like #136. I propose to change the slugger completely and accept any character.

For example, you can now create this blog post:

![backend_post](https://cloud.githubusercontent.com/assets/73419/19352609/b582a714-9160-11e6-81de-8e5130f1ec78.png)

And the blog listing no longer displays an error:

![blog_post](https://cloud.githubusercontent.com/assets/73419/19352619/bfbd87d0-9160-11e6-89fa-ca60aee1b5fe.png)

And the URL is perfectly fine although it contains non-Latin chars:

![url-post](https://cloud.githubusercontent.com/assets/73419/19352634/c9fc89c6-9160-11e6-999c-346b4da78653.png)

Commits
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161b508 Made the slugger compatible with every language

Author: javiereguiluz

src/AppBundle/Utils/Slugger.php

@@ -27,6 +27,6 @@ class Slugger
      */
     public function slugify($string)
     {
-        return trim(preg_replace('/[^a-z0-9]+/', '-', strtolower(strip_tags($string))), '-');
+        return preg_replace('/\s+/', '-', mb_strtolower(trim(strip_tags($string)), 'UTF-8'));
     }
 }

tests/AppBundle/Utils/SluggerTest.php

@@ -38,10 +38,13 @@ public function testSlugify($string, $slug)
 
     public function getSlugs()
     {
-        yield ['Lorem Ipsum'     , 'lorem-ipsum'];
-        yield ['  Lorem Ipsum  ' , 'lorem-ipsum'];
-        yield [' lOrEm  iPsUm  ' , 'lorem-ipsum'];
-        yield ['!Lorem Ipsum!'   , 'lorem-ipsum'];
-        yield ['lorem-ipsum'     , 'lorem-ipsum'];
+        yield ['Lorem Ipsum', 'lorem-ipsum'];
+        yield ['  Lorem Ipsum  ', 'lorem-ipsum'];
+        yield [' lOrEm  iPsUm  ', 'lorem-ipsum'];
+        yield ['!Lorem Ipsum!', '!lorem-ipsum!'];
+        yield ['lorem-ipsum', 'lorem-ipsum'];
+        yield ['lorem 日本語 ipsum', 'lorem-日本語-ipsum'];
+        yield ['lorem русский язык ipsum', 'lorem-русский-язык-ipsum'];
+        yield ['lorem العَرَبِيَّة‎‎ ipsum', 'lorem-العَرَبِيَّة‎‎-ipsum'];
     }
 }