Rename Server- and ClientMessage

Renamed ServerMessage and ClientMessage to respectively ResponseMessage
and RequestMessage to make it more clear.

httplib/message.py

@@ -16,7 +16,7 @@ class Message(ABC):
         self.body = body
 
 
-class ClientMessage(Message):
+class ResponseMessage(Message):
     status: int
     msg: str
 
@@ -26,7 +26,7 @@ class ClientMessage(Message):
         self.msg = msg
 
 
-class ServerMessage(Message):
+class RequestMessage(Message):
     method: str
     target: SplitResult