Convert escapers to singletons (#239)

src/Spout/Reader/XLSX/Helper/CellValueFormatter.php

@@ -62,7 +62,7 @@ class CellValueFormatter
         $this->shouldFormatDates = $shouldFormatDates;
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $this->escaper = new \Box\Spout\Common\Escaper\XLSX();
+        $this->escaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
     }
 
     /**

src/Spout/Reader/XLSX/Helper/SharedStringsHelper.php

@@ -80,7 +80,7 @@ class SharedStringsHelper
         $xmlReader = new XMLReader();
         $sharedStringIndex = 0;
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $escaper = new \Box\Spout\Common\Escaper\XLSX();
+        $escaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
 
         $sharedStringsFilePath = $this->getSharedStringsFilePath();
         if ($xmlReader->open($sharedStringsFilePath) === false) {

src/Spout/Reader/XLSX/Helper/SheetHelper.php

@@ -87,7 +87,7 @@ class SheetHelper
         $escapedSheetName = $xmlReaderOnSheetNode->getAttribute('name');
 
         /** @noinspection PhpUnnecessaryFullyQualifiedNameInspection */
-        $escaper = new \Box\Spout\Common\Escaper\XLSX();
+        $escaper = \Box\Spout\Common\Escaper\XLSX::getInstance();
         $sheetName = $escaper->unescape($escapedSheetName);
 
         $sheetDataXMLFilePath = $this->getSheetDataXMLFilePathForSheetId($sheetId);