Added worksheet_set_top_left_cell() function.

Added worksheet_set_top_left_cell() function to set the first
visible cell in the worksheet.

test/functional/src/test_top_left_cell01.c

@@ -0,0 +1,20 @@
+/*****************************************************************************
+ * Test cases for libxlsxwriter.
+ *
+ * Test to compare output against Excel files.
+ *
+ * Copyright 2014-2021, John McNamara, jmcnamara@cpan.org
+ *
+ */
+
+#include "xlsxwriter.h"
+
+int main() {
+
+    lxw_workbook  *workbook  = workbook_new("test_top_left_cell01.xlsx");
+    lxw_worksheet *worksheet = workbook_add_worksheet(workbook, NULL);
+
+    worksheet_set_top_left_cell(worksheet, 15, 0);
+
+    return workbook_close(workbook);
+}

test/functional/src/test_top_left_cell02.c

@@ -0,0 +1,20 @@
+/*****************************************************************************
+ * Test cases for libxlsxwriter.
+ *
+ * Test to compare output against Excel files.
+ *
+ * Copyright 2014-2021, John McNamara, jmcnamara@cpan.org
+ *
+ */
+
+#include "xlsxwriter.h"
+
+int main() {
+
+    lxw_workbook  *workbook  = workbook_new("test_top_left_cell02.xlsx");
+    lxw_worksheet *worksheet = workbook_add_worksheet(workbook, NULL);
+
+    worksheet_set_top_left_cell(worksheet, 15, 6);
+
+    return workbook_close(workbook);
+}

test/functional/src/test_top_left_cell03.c

@@ -0,0 +1,20 @@
+/*****************************************************************************
+ * Test cases for libxlsxwriter.
+ *
+ * Test to compare output against Excel files.
+ *
+ * Copyright 2014-2021, John McNamara, jmcnamara@cpan.org
+ *
+ */
+
+#include "xlsxwriter.h"
+
+int main() {
+
+    lxw_workbook  *workbook  = workbook_new("test_top_left_cell03.xlsx");
+    lxw_worksheet *worksheet = workbook_add_worksheet(workbook, NULL);
+
+    worksheet_set_top_left_cell(worksheet, CELL("AA32"));
+
+    return workbook_close(workbook);
+}

test/functional/test_top_left_cell.py

@@ -0,0 +1,24 @@
+###############################################################################
+#
+# Tests for libxlsxwriter.
+#
+# Copyright 2014-2021, John McNamara, jmcnamara@cpan.org
+#
+
+import base_test_class
+
+class TestCompareXLSXFiles(base_test_class.XLSXBaseTest):
+    """
+    Test file created with libxlsxwriter against a file created by Excel.
+
+    """
+
+    def test_top_left_cell01(self):
+        self.run_exe_test('test_top_left_cell01')
+
+    def test_top_left_cell02(self):
+        self.run_exe_test('test_top_left_cell02')
+
+    def test_top_left_cell03(self):
+        self.run_exe_test('test_top_left_cell03')
+