Preserve blank lines between comments and surrounding syntax elements

[ennocramer]

Follow up for issue #19.

Implement logic to preserve spacing around comments as in

function1 = undefined

--

function2 = undefined

The current output is

function1 = undefined

--
function2 = undefined

[Rhywun]

Thanks - I'll remember to keep issues separate next time!

[domenkozar]

I'm not sure if this is the same issue but:

foo = do
    {- blab la -}
    bar <- command
    bar

is formatted to

foo = do
    {- blab la -}bar <- command
    bar

which is clearly a syntax error.