Simple higher order function for Maybe.

Maybe you just need justify?

We've all used Maybe in a control flow

if f x then Just x else Nothing

but why not have

justify id f x

multiple constraints?

justify id (\a -> f a && g a) x

want a silly id for Maybe?

justify fromJust isJust (Just x)

This seems like such a no brainer that I'm surprised it isn't in Data.Maybe so I'm proposing that it should be and this library is just the start.

What about licensing issues?

Since I know there will be some talk about licensing, I already took the step and used the unlicense. If that isn't enough, just send a pull request changing it to an appropriate license and I'll accept.

What do I do while this isn't in Data.Maybe?

Then just go ahead and pull in maybe-justify from cabal!