Issue 156: update SZip and ScaleOffset enums

[jkotan]

It resolves #156 by updating SZip and ScaleOffset enums

One test fails

self = <test.h5cpp_tests.node_tests.dataset_extent_test.DatasetExtentTest testMethod=testGrowExtentLimited>

    def testGrowExtentLimited(self):
    
        dataset = Dataset(self.root, h5cpp.Path("GrowExtentLimited"),
                          kFloat32,
                          self.limited_dataspace,
                          self.lcpl,
                          self.dcpl)
        dataset.extent(0, 10)
        self.assertEqual(dataset.dataspace.current_dimensions, (20, 10))
    
        self.assertRaises(RuntimeError, dataset.extent, 0, 90)
        self.assertRaises(RuntimeError, dataset.extent, 1, 1)
        self.assertEqual(dataset.dataspace.current_dimensions, (20, 10))
    
        #
        # shrink the dataset again
        #
>       dataset.extent(0, -2)
E       RuntimeError: input value is < 0 -> cannot be converted to unsigned

test/h5cpp_tests/node_tests/dataset_extent_test.py:121: RuntimeError

but it is related to ess-dmsc/h5cpp#568 and will be fixed by ess-dmsc/h5cpp#569