Issue #1 建立 Double 序列初始版本

src/Helpers/SequenceCalculator/DoubleSequenceCalculator.php

@@ -0,0 +1,28 @@
+<?php
+/**
+ * Created by PhpStorm.
+ * User: mouson
+ * Date: 2017/1/10
+ * Time: 03:44
+ */
+
+namespace Mouson\Helpers\SequenceCalculator;
+
+class DoubleSequenceCalculator implements CalculatorInterface
+{
+
+    /**
+     * @param $value
+     *
+     * @return int|mixed
+     */
+    public function calculate($value)
+    {
+        return ($value * 2);
+    }
+
+    public function getSequenceName()
+    {
+        return 'Double';
+    }
+}