Add filters and class based handler for errors

docs/dispatcher/class_based_handlers/error.md

@@ -0,0 +1,29 @@
+# ErrorHandler
+
+There is base class for error handlers.
+
+## Simple usage:
+```pyhton3
+from aiogram.handlers import ErrorHandler
+
+...
+
+@router.errors_handler()
+class MyHandler(ErrorHandler):
+    async def handle(self) -> Any:
+        log.exception(
+            "Cause unexpected exception %s: %s", 
+            self.event.__class__.__name__, 
+            self.event
+        )
+```
+
+## Extension
+
+This base handler is subclass of [BaseHandler](basics.md#basehandler)
+
+## Related pages
+
+- [BaseHandler](basics.md#basehandler)
+- [Router.errors_handler](../router.md#errors)
+- [Filters](../filters/exception.md)