Merge in ghc-lib-parser patches

[jaspervdj]

This is an integration PR to merge #293 and the GSOC work. There are still
a number of backwards-incompatible changes that need to be sorted out
before we can fully release this, and I'll keep notes of any significant changes
here.

Changes

• I changed the sorting order of imported things back to the following order:
  constructors/data types/classes, followed by functions, followed by operators.

• I changed the grouping of imports to check for consecutive lines of imports
  rather than using comments as separators (but comments should still be
  preserved, of course).

• The Imports step is not taking the global alignment option into account.

• The printer code seems unequipped to do proper wrapping: it decides
  whether or not to print a newline by looking at the current line length, rather
  than the hypothetical line length if a comma, space and the next item are
  added.

  Looking at the printer code, it should be possible to add a combinator along
  the lines of:

  ifFitsOnLine
      :: P a  -- ^ Code that appends to the line, should not print a newline
      -> P a  -- ^ Code executed if the previous code surpasses line length
      -> P a  -- ^ Result of left or right branch
  

• I think there is still an off-by-one error in the import wrapping code: it
  doesn't take the final , into account.

• The style of consecutive lines for a single import has changed from

  import Data.List (init, last,
                    head)
  

  to:

  import Data.List (init, last)
  import Data.List (head)
  

  I'd like to revert the default back to the original but we'll want to retain the
  new style as an option. Proposal is to add the new style as
  list_align: repeat.

  Note that this also involves adding all the other options here that list_align
  supports.

• There are many more issues with various combinations of long_list_align,
  list_align, space_surround and align.

• The Align step is having trouble with many files, for example:

  foo = align
    where
      align' = importAlign align
      padModuleNames' = padModuleNames align
      padNames = align' /= None && padModuleNames'
      padQual  = case align' of
        Global -> True
        File   -> fileAlign
        Group  -> anyQual
        None   -> False
  

• The ModuleHeader step should allow configuring indentation

• The ModuleHeader step should allow turning off sorting

• The ModuleHeader step should use the same sorting order as Imports

• The LanguagePragmas step is still using haskell-src-exts

• The UnicodeSyntax step is still using haskell-src-exts

Open issues

[jaspervdj]

Merged in 250e709, thanks again to everyone involved!