Add Delay for Reddit support

Adds support for delayforreddit.com non-direct links.

tests/site_downloaders/test_delay_for_reddit.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python3
+# coding=utf-8
+
+from unittest.mock import Mock
+
+import pytest
+
+from bdfr.resource import Resource
+from bdfr.site_downloaders.delay_for_reddit import DelayForReddit
+
+
+@pytest.mark.online
+@pytest.mark.parametrize(('test_url', 'expected_hash'), (
+    ('https://www.delayforreddit.com/dfr/calvin6123/MjU1Njc5NQ==', '3300f28c2f9358d05667985c9c04210d'),
+    ('https://www.delayforreddit.com/dfr/RoXs_26/NDAwMzAyOQ==', '09b7b01719dff45ab197bdc08b90f78a'),
+))
+def test_download_resource(test_url: str, expected_hash: str):
+    mock_submission = Mock()
+    mock_submission.url = test_url
+    test_site = DelayForReddit(mock_submission)
+    resources = test_site.find_resources()
+    assert len(resources) == 1
+    assert isinstance(resources[0], Resource)
+    resources[0].download()
+    assert resources[0].hash.hexdigest() == expected_hash