Replaced vendored openpyxl by a dependency (#221)

It is time to make it happen.

* Dropped Python 3.2 support

Recent dependencies are dropping Python 3.2 too.

* Replaced vendored openpyxl by a dependency

Thanks Tommy Anthony for the initial patch.

test_tablib.py

@@ -956,6 +956,11 @@ class TablibTestCase(unittest.TestCase):
         """Test XLSX export with formatter configuration."""
         self.founders.export('xlsx', freeze_panes=False)
 
+    def test_databook_formatter_with_new_lines(self):
+        """Test XLSX export with new line in content."""
+        self.founders.append(('First\nSecond', 'Name', 42))
+        self.founders.export('xlsx')
+
 
 if __name__ == '__main__':
     unittest.main()