Special characters handling

* Fix README for python version
* Add discord-friendly unidecode function for channel names (avoiding
  special characted)
* Check if "items" is present before accessing in channel id request
  response

tests/test_unidecode.py

@@ -0,0 +1,14 @@
+from breadtube_bot.unidecode import unidecode
+
+
+def test_unidecode():
+    test_data = [
+        ('éêçà', 'eeca'),
+        ('あいうえお', 'aiueo'),
+        ('アイウエオ', 'aiueo'),
+        ('ČŽŠčžš', 'czsczs'),
+        ('?! .,<', '______'),
+    ]
+    for data, expected in test_data:
+        result = unidecode(data)
+        assert result == expected, f'Wrong result for "{data}": got "{result}", expected "{expected}"'