Add support for multiline strings

Escaped line feed characters in shared strings before processing them.
This makes every string remain on one single line and therefore allow
fast retrieval
Replaced usages of "\n" by PHP_EOL
Added test for multiline strings

tests/Spout/Reader/Helper/XLSX/SharedStringsHelperTest.php

@@ -46,7 +46,7 @@ class SharedStringsHelperTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals(1, count($filesInTempFolder), 'One temp file should have been created in the temp folder.');
 
         $tempFileContents = file_get_contents($filesInTempFolder[0]);
-        $tempFileContentsPerLine = explode("\n", $tempFileContents);
+        $tempFileContentsPerLine = explode(PHP_EOL, $tempFileContents);
 
         $this->assertEquals('s1--A1', $tempFileContentsPerLine[0]);
         $this->assertEquals('s1--E5', $tempFileContentsPerLine[24]);
@@ -96,4 +96,23 @@ class SharedStringsHelperTest extends \PHPUnit_Framework_TestCase
         $sharedString = $this->sharedStringsHelper->getStringAtIndex(24);
         $this->assertEquals('s1--E5', $sharedString);
     }
+
+    /**
+     * @return void
+     */
+    public function testGetStringAtIndexShouldWorkWithMultilineStrings()
+    {
+        $resourcePath = $this->getResourcePath('one_sheet_with_shared_multiline_strings.xlsx');
+        $sharedStringsHelper = new SharedStringsHelper($resourcePath);
+
+        $sharedStringsHelper->extractSharedStrings();
+
+        $sharedString = $sharedStringsHelper->getStringAtIndex(0);
+        $this->assertEquals("s1\nA1", $sharedString);
+
+        $sharedString = $sharedStringsHelper->getStringAtIndex(24);
+        $this->assertEquals("s1\nE5", $sharedString);
+
+        $sharedStringsHelper->cleanup();
+    }
 }

tests/Spout/Writer/CSVTest.php

@@ -135,6 +135,6 @@ class CSVTest extends \PHPUnit_Framework_TestCase
     private function trimWrittenContent($writtenContent)
     {
         // remove line feeds and UTF-8 BOM
-        return trim($writtenContent, "\n" . CSV::UTF8_BOM);
+        return trim($writtenContent, PHP_EOL . CSV::UTF8_BOM);
     }
 }