Empty lines inserted between `type instance` clauses

[andreasabel]

hindent (current master) turns this:

-- Just like a class can get new instances,
-- an open type family can always get new clauses:

type instance Le Bot     Bot     = ()
type instance Le Bot     (Emb y) = ()
type instance Le Bot     Top     = ()
type instance Le (Emb x) Bot     = Empty
type instance Le (Emb x) Top     = ()
type instance Le (Emb x) (Emb y) = Le x y
type instance Le Top     (Emb y) = Empty
type instance Le Top     Bot     = Empty
type instance Le Top     Top     = ()

into this:

-- Just like a class can get new instances,
-- an open type family can always get new clauses:
type instance Le Bot Bot = ()

type instance Le Bot (Emb y) = ()

type instance Le Bot Top = ()

type instance Le (Emb x) Bot = Empty

type instance Le (Emb x) Top = ()

type instance Le (Emb x) (Emb y) = Le x y

type instance Le Top (Emb y) = Empty

type instance Le Top Bot = Empty

type instance Le Top Top = ()

Not sure why it would be desireable to have empty lines between the type instance clauses.

P.S.: I am not a user of hindent, I just saw the project and tried it out on one of my files.