Deriving alignment for enums

[Lev135]

Fixes #411

I've changed printer's behavior for alignment of deriving closes: now it adds newline and indentation before deriving even if onelineEnum is enabled:

data Foo = A | B | C
  deriving (Eq, Show)

instead of

data Foo = A | B | C deriving (Eq, Show)

This behavior is what is said in docs:

Deriving clauses are always on separate lines

Surely we can add an option to preserve the previous behavior, but I don't think that it's desired for several reasons:

• it conflicts with docs
• it leads to an awful output when enum is large, that even not highlight well:

data DefType = DefTEnv | DefTPref | DefTCmd | DefTInl | DefTMode | DefTSort deriving
    ( Eq
    , Ord
    , Show
    )

However, if you think otherwise, I can add an option. Maybe while break_enums option was discussed the reasons of this choice were expained, but I couldn't find anything.

Only two tests were affected by this change:

• case 20 (establish the break_enums option)

Before:

data Tag = Title | Text deriving (Eq, Show)

After:

data Tag = Title | Text 
  deriving (Eq, Show)

• case 55 (issue Enum formatting #262, not related to deriving problem)

Before:

data Foo = Foo deriving (Z, Y, X, Bar, Abcd)

After:

data Foo = Foo 
  deriving (Z, Y, X, Bar, Abcd)

[Lev135]

Oh, I've found related issue: #379. I think it should be closed by this pull request