[feature request] Support for defined number of blank lines between top-level declarations

[0rphee]

After using elm-format (the standard elm formatter) I realized that it would be convenient to have the option to enable a defined number of blank lines between top-level declarations, to avoid having places where there is inconsistent spacing between declarations and minimize diffs when refactoring and adding new code.

(I looked through issues and the default config file for an already existing option to enable this, without finding anything)

Hopefully with this option, stylish-haskell would change this:

fun :: Num a => a -> a -> a
fun a b = a + b
gun :: t
gun = gun



i :: Integer
i = 0

o :: Integer
o = 0

To this (assuming a 2 blank-line separation between declarations):

fun :: Num a => a -> a -> a
fun a b = a + b


gun :: t
gun = gun


i :: Integer
i = 0


o :: Integer
o = 0