Fix pickle

Saving as pickle was failing for me because the extension was still unknown to parts of the code.

I fixed some documentation and removed the unused gzip argument from Result.__init__

We should add some tests as well before we merge this in.

test/core/result_test.py

@@ -230,15 +230,14 @@ class TestResult(unittest.TestCase):
     def test_save_and_dont_overwrite(self):
         extensions = ['json', 'pkl', 'hdf5']
         for extension in extensions:
-            shutil.rmtree(f"{self.result.outdir}/{self.result.label}_result.{extension}.old", ignore_errors=True)
-            self.result.save_to_file(overwrite=False)
-            self.result.save_to_file(overwrite=False)
+            print(extension)
+            self.result.save_to_file(overwrite=False, extension=extension)
+            self.result.save_to_file(overwrite=False, extension=extension)
             self.assertTrue(os.path.isfile(f"{self.result.outdir}/{self.result.label}_result.{extension}.old"))
 
     def test_save_and_overwrite_default(self):
         extensions = ['json', 'pkl', 'hdf5']
         for extension in extensions:
-            shutil.rmtree(f"{self.result.outdir}/{self.result.label}_result.{extension}.old", ignore_errors=True)
             self.result.save_to_file(overwrite=True, extension=extension)
             self.result.save_to_file(overwrite=True, extension=extension)
             self.assertFalse(os.path.isfile(f"{self.result.outdir}/{self.result.label}_result.{extension}.old"))