Line breaking support for function definitions

[Ailrun]

When there is a definition like

myFun :: a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a
myFun = undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined undefined

Stylish-haskell doesn't touch this definition even with columns: 80 config. It will be great if stylish-haskell can format this kind of long expression and gives something like

myFun :: a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a -> a
  -> a -> a -> a -> a -> a -> a -> a -> a -> a
myFun = undefined undefined undefined undefined undefined undefined undefined
  undefined undefined undefined undefined