Dev 3.x flat package (#961)

* Move packages

* Added changelog

* Update examples/echo_bot.py

Co-authored-by: Oleg A. <t0rr@mail.ru>

* Rename `handler` -> `handlers`

* Update __init__.py

Co-authored-by: Oleg A. <t0rr@mail.ru>

tests/test_handler/test_chat_member.py

@@ -0,0 +1,29 @@
+import datetime
+from typing import Any
+
+import pytest
+
+from aiogram.handlers import ChatMemberHandler
+from aiogram.types import Chat, ChatMemberMember, ChatMemberUpdated, User
+
+pytestmark = pytest.mark.asyncio
+
+
+class TestChatMemberUpdated:
+    async def test_attributes_aliases(self):
+        event = ChatMemberUpdated(
+            chat=Chat(id=42, type="private"),
+            from_user=User(id=42, is_bot=False, first_name="Test"),
+            date=datetime.datetime.now(),
+            old_chat_member=ChatMemberMember(user=User(id=42, is_bot=False, first_name="Test")),
+            new_chat_member=ChatMemberMember(user=User(id=42, is_bot=False, first_name="Test")),
+        )
+
+        class MyHandler(ChatMemberHandler):
+            async def handle(self) -> Any:
+                assert self.event == event
+                assert self.from_user == self.event.from_user
+
+                return True
+
+        assert await MyHandler(event)