Moved constants to its own file inside config folder

config/constants.php

@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink;
+
+use Fig\Http\Message\StatusCodeInterface;
+
+const DEFAULT_DELETE_SHORT_URL_THRESHOLD = 15;
+const DEFAULT_SHORT_CODES_LENGTH = 5;
+const MIN_SHORT_CODES_LENGTH = 4;
+const DEFAULT_REDIRECT_STATUS_CODE = StatusCodeInterface::STATUS_FOUND;
+const DEFAULT_REDIRECT_CACHE_LIFETIME = 30;
+const LOCAL_LOCK_FACTORY = 'Shlinkio\Shlink\LocalLockFactory';
+const CUSTOM_SLUGS_REGEXP = '/[^\pL\pN._~]/u'; // Any unicode letter or number, plus ".", "_" and "~" chars
+const TITLE_TAG_VALUE = '/<title[^>]*>(.*?)<\/title>/i'; // Matches the value inside an html title tag