Add safe functions to work with 'Enum'

[chshersh]

Sometimes it's useful to have the following functions:

every      :: (Bounded a, Enum a) => [a]  -- all values
cycleSucc  :: (Bounded a, Enum a) => a -> a  -- like succ, but doesn't fail on maxBound
safeToEnum :: Enum a => Int -> Maybe a  -- Nothing if Int outside enum range

Maybe something else...

[dcastro]

I would also add:

• cyclePred
• safeSucc :: a -> Maybe a and safePred :: a -> Maybe a

Just as safeToEnum is useful for when a is "narrower" than Int (e.g. toEnum @Word8 maxBound will throw), we should also have safeFromEnum for when a is "wider" than Int (e.g. fromEnum @Word64 maxBound will also throw)