Expose a Sheet object on Reader::XLSX::nextSheet()

Added Sheet class for the XLSX reader that exposes basic sheet info, such as name or ID.
When retrieving the sheet data XML, added extra XML parsing to retrieve sheet data.
Added test

src/Spout/Common/Helper/GlobalFunctionsHelper.php

@@ -119,7 +119,7 @@ class GlobalFunctionsHelper
      * Wrapper around global function file_exists()
      * @see file_exists()
      *
-     * @param string $filename
+     * @param string $fileName
      * @return bool
      */
     public function file_exists($fileName)
@@ -127,11 +127,23 @@ class GlobalFunctionsHelper
         return file_exists($fileName);
     }
 
+    /**
+     * Wrapper around global function file_get_contents()
+     * @see file_get_contents()
+     *
+     * @param string $filePath
+     * @return bool
+     */
+    public function file_get_contents($filePath)
+    {
+        return file_get_contents($filePath);
+    }
+
     /**
      * Wrapper around global function is_readable()
      * @see is_readable()
      *
-     * @param string $filename
+     * @param string $fileName
      * @return bool
      */
     public function is_readable($fileName)
@@ -144,11 +156,12 @@ class GlobalFunctionsHelper
      * @see basename()
      *
      * @param string $path
+     * @param string|void $suffix
      * @return string
      */
-    public function basename($path)
+    public function basename($path, $suffix = null)
     {
-        return basename($path);
+        return basename($path, $suffix);
     }
 
     /**