Fix "WHERE bracketing bug", detailed at https://github.com/m4dc4p/haskelldb/issues/14
Support "UNION ALL" in the AST (although not exported to Query API)
Fix some parenthesization issues for BinExpr and prefix UnExpr:

* The default for BinExpr should be to parenthesize both branches.
* Constant expressions do not need to be parenthesized.
* Prefix UnExprs may need to be parenthesized, e.g. it should be
    NOT (TRUE AND TRUE)
  rather than
    NOT TRUE AND TRUE;
  For safety this patch parenthesizes all prefix UnExprs.
Use the 'parens' combinator from 'Text.PrettyPrint.HughesPJ' rather than
reimplementing it.
Export unionAll from Database.HaskellDB.Query
Merge pull request #19 from tomjaguarpaw/master

Fix "WHERE" bracketing bug and "UNION ALL"