additions to Data.Map

I'd like to propose the following additions to Data.Map (and IntMap): -- | /O(n)/. Map values and collect the 'Just' results. mapMaybe :: Ord k => (a -> Maybe b) -> Map k a -> Map k b -- | /O(n)/. Map keys\/values and collect the 'Just' results. mapMaybeWithKey :: Ord k => (k -> a -> Maybe b) -> Map k a -> Map k b -- | /O(n)/. Map values and separate the 'Left' and 'Right' results. mapEither :: Ord k => (a -> Either b c) -> Map k a -> (Map k b, Map k c) -- | /O(n)/. Map keys\/values and separate the 'Left' and 'Right' results. mapEitherWithKey :: Ord k => (k -> a -> Either b c) -> Map k a -> (Map k b, Map k c)