More class based handlers

docs/dispatcher/class_based_handlers/poll.md

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+# PollHandler
+
+There is base class for poll handlers.
+
+## Simple usage:
+```pyhton3
+from aiogram.handlers import PollHandler
+
+...
+
+@router.poll_handler()
+class MyHandler(PollHandler):
+    async def handle(self) -> Any: ...
+
+```
+
+## Extension
+
+This base handler is subclass of [BaseHandler](basics.md#basehandler) with some extensions:
+
+- `self.question` is alias for `self.event.question`
+- `self.options` is alias for `self.event.options`
+
+## Related pages
+
+- [BaseHandler](basics.md#basehandler)
+- [Poll](../../api/types/poll.md)
+- [Router.poll_handler](../router.md#poll)