Upgrade architecture + 5.0 Bot API (#469)

Upgrade architecture + 5.0 Bot API (#469)
* Moved `methods`, `types` and `client` to root package
* Removed update handler from routers to dispatcher
* Reworked events propagation mechanism to handlers
* Reworked inner middlewares logic (very small change)
* Updated to Bot API 5.0
* Initial migration from MkDocs to Sphinx + config for readthedocs

examples/echo_bot.py

@@ -0,0 +1,41 @@
+from typing import Any
+
+from aiogram import Bot, Dispatcher, types
+from aiogram.dispatcher.handler import MessageHandler
+
+TOKEN = "42:TOKEN"
+dp = Dispatcher()
+
+
+@dp.message(commands=["start"])
+class MyHandler(MessageHandler):
+    """
+    This handler receive messages with `/start` command
+
+    Usage of Class-based handlers
+    """
+
+    async def handle(self) -> Any:
+        await self.event.answer(f"<b>Hello, {self.from_user.full_name}!</b>")
+
+
+@dp.message(content_types=[types.ContentType.ANY])
+async def echo_handler(message: types.Message, bot: Bot) -> Any:
+    """
+    Handler will forward received message back to the sender
+
+    Usage of Function-based handlers
+    """
+
+    await bot.forward_message(
+        from_chat_id=message.chat.id, chat_id=message.chat.id, message_id=message.message_id
+    )
+
+
+def main() -> None:
+    bot = Bot(TOKEN, parse_mode="HTML")
+    dp.run_polling(bot)
+
+
+if __name__ == "__main__":
+    main()