Update Writer folder structure to match Reader new structure

src/Spout/Writer/XLSX/Sheet.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace Box\Spout\Writer\XLSX;
+
+/**
+ * Class Sheet
+ * Represents a worksheet within a XLSX file
+ *
+ * @package Box\Spout\Writer\XLSX
+ */
+class Sheet
+{
+    const DEFAULT_SHEET_NAME_PREFIX = 'Sheet';
+
+    /** @var int Index of the sheet, based on order of creation (zero-based) */
+    protected $index;
+
+    /** @var string Name of the sheet */
+    protected $name;
+
+    /**
+     * @param int $sheetIndex Index of the sheet, based on order of creation (zero-based)
+     */
+    function __construct($sheetIndex)
+    {
+        $this->index = $sheetIndex;
+        $this->name = self::DEFAULT_SHEET_NAME_PREFIX . ($sheetIndex + 1);
+    }
+
+    /**
+     * @return int Index of the sheet, based on order of creation (zero-based)
+     */
+    public function getIndex()
+    {
+        return $this->index;
+    }
+
+    /**
+     * @return string Name of the sheet
+     */
+    public function getName()
+    {
+        return $this->name;
+    }
+
+    /**
+     * @param string $name Name of the sheet
+     * @return Sheet
+     */
+    public function setName($name)
+    {
+        $this->name = $name;
+        return $this;
+    }
+}