Remove dead pretty-printing code that is duplicated anyway.
Fix #1788

- Remove redundant space after `description:` field name.
- Eliminate trailing spaces on *some* blank lines.
- Convert all field names to lower case.
- Eliminate redundant `buildable: True` and `exposed: True` fields.
- Fix Haddock module comment.
Merge remote-tracking branch 'upstream/master' into cabal-format
Pretty-printing: improve omission of defaults

Consolidate default values and make flag pretty-printing use them.
Allow code to work with non-boolean defaults.
Add comment about temporary fix for pretty-printing defaults
Merge branch 'cabal-format' of https://github.com/ianbollinger/cabal