Takes specified keys from an association; supports the operator form KeyTake[keys][assoc]
KeyTake[assoc, {key1, key2, …}]
KeyTake[{assoc1, assoc2, …}, keys]
KeyTake[{key1, key2, …}]
KeyTake[<|a -> 1, b -> 2, c -> 3|>, {a, c}]
→ <|a -> 1, c -> 3|>KeyTake[{a, c}][<|a -> 1, b -> 2, c -> 3|>]
→ <|a -> 1, c -> 3|>