improved code styles #158 (#172)

* use php-cs-fixer instead of phpcodesniffer
* updated scrutinizer config
* adjusted code yules to all files
* updated CONTRIBUTING guidelines

tests/Twig/MarkdownExtensionTest.php

@@ -18,7 +18,6 @@ use PHPUnit\Framework\TestCase;
  */
 class MarkdownExtensionTest extends TestCase
 {
-
     public function testGetFilters()
     {
         $sut = new MarkdownExtension(new Markdown());