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/Utils/DurationTest.php

@@ -17,7 +17,6 @@ use PHPUnit\Framework\TestCase;
  */
 class DurationTest extends TestCase
 {
-
     public function testFormat()
     {
         $sut = new Duration();

tests/Utils/MarkdownTest.php

@@ -17,7 +17,6 @@ use PHPUnit\Framework\TestCase;
  */
 class MarkdownTest extends TestCase
 {
-
     public function testMarkdownToHtml()
     {
         $sut = new Markdown();