Add Pointed instances to types from kan-extensions

[mstksg]

Thank you for the great library :)

Just a small patch that adds Pointed instances for all of the types from kan-extensions that I could imagine instances for. For those that are Applicative, I believe pure = pointed.

Let me know if there's anything I can fix in this :)

[mstksg]

I did notice something weird; Co could get a Pointed instance if the lifted comonad was Copointed, I believe, but this is tricky because neither module seems to imports the other, so such an instance is not possible without an asymmetric import.