Added middlewares.

Bumped middlewares

telebot/handler_backends.py

@@ -165,4 +165,43 @@ class StatesGroup:
                 # change value of that variable
                 value.name = ':'.join((cls.__name__, name))
 
-    
+    
+class BaseMiddleware:
+    """
+    Base class for middleware.
+    Your middlewares should be inherited from this class.
+    """
+
+    def __init__(self):
+        pass
+
+    def pre_process(self, message, data):
+        raise NotImplementedError
+
+    def post_process(self, message, data, exception):
+        raise NotImplementedError
+
+
+class SkipHandler:
+    """
+    Class for skipping handlers.
+    Just return instance of this class 
+    in middleware to skip handler.
+    Update will go to post_process,
+    but will skip execution of handler.
+    """
+
+    def __init__(self) -> None:
+        pass
+
+class CancelUpdate:
+    """
+    Class for canceling updates.
+    Just return instance of this class 
+    in middleware to skip update.
+    Update will skip handler and execution
+    of post_process in middlewares.
+    """
+
+    def __init__(self) -> None:
+        pass