Abstract factory (#366)

* rewrite of the Abstract Factory pattern

* update composer deps

* fixed argument to json_encode which cannot be null

Creational/AbstractFactory/WriterFactory.php

@@ -0,0 +1,9 @@
+<?php
+
+namespace DesignPatterns\Creational\AbstractFactory;
+
+interface WriterFactory
+{
+    public function createCsvWriter(): CsvWriter;
+    public function createJsonWriter(): JsonWriter;
+}