Resolve "Introduce PSR-4 autoloading"

Closes #12

tests/UtilsTest.php

@@ -115,7 +115,7 @@ final class UtilsTest extends TestCase
             'media-type' => '',
         ],
         'Plain text' => [
-          'expected' => 'html',
+          'expected' => 'nt',
           'media-type' => 'text/plain',
         ],
         'CSS request' => [
@@ -127,11 +127,11 @@ final class UtilsTest extends TestCase
           'media-type' => 'application/json',
         ],
         'Illegal JSON' => [
-          'expected' => 'json',
+          'expected' => 'html',
           'media-type' => 'application/jsons',
         ],
         'Image jpeg' => [
-          'expected' => 'json',
+          'expected' => 'html',
           'media-type' => 'image/jpeg',
         ],
       ];