rethought --relaxed change

Better to make it not be surprising and slow, than surprising and fast.
--raw can be used when it needs to be really fast.

Implemented adding a youtube-dl supported url to an existing file.

This commit was sponsored by andrea rota.

Types/Transfer.hs

@@ -87,7 +87,7 @@ instance Observable (Either e Bool) where
 	observeBool (Right b) = b
 	observeFailure = Right False
 
-instance Observable (Either e (Maybe a)) where
-	observeBool (Right (Just _)) = True
-	observeBool _ = False
-	observeFailure = Right Nothing
+instance Observable (Maybe a) where
+	observeBool (Just _) = True
+	observeBool Nothing = False
+	observeFailure = Nothing