Add ifThenElse and (?) to Data.Bool

[Henning Thielemann]

On Thu, 17 Nov 2016, winter wrote:

> Ah Yeah, i see. It’s indeed a rare use case.
> From all your feedback, I guess i will make a package with (?) for someone who want to save keystrokes like me ;)

I use if' and (?:) from
    https://hackage.haskell.org/package/utility-ht-0.0.12/docs/Data-Bool-HT.html

E.g. this is very handy:
    if' (even n) "even" $
    if' (isPrime n) "prime" $
    "boring"

(?:) is the uncurried variant of (?). I do not see value in curried (?) 
because I can just use `if'` then (which I never did).