Log Message:
Update to 0.6.7

changes:
0.6.7
 - Merge pull request #5 from sjindel/master
   * Several algorithmic improvements to the Wadler-Leijen
   pretty-printing algorithm.
    1) Addition of the @Fail@ primitive, representing a document that can not be
       rendered. @Fail@ is a left unit of @Union@ and does not `fit' into any page
       width. It allows the construction of documents that can not be flattened, for
       example comments that must be followed by a newline. It also alows the
       construction of hard lines, which are guaranteed to be rendered as a newline.
    2) Addition of the @FlatAlt@ primitive, representing a document which changes
       under flattening. This unifies the linebreak combinators and allows for more
       flexible linebreak to be created, for example linebreaks in a do-block that
       should become semicolons when flattened.
    3) Addition of a more intelligent rendering algorithm, which partially solves
       the lookahead problem caused by deeply nested structures where a single-line
       lookahead will not always allow a document to be formatted within the
       pagewidth.
 ( #5 => https://github.com/batterseapower/ansi-wl-pprint/pull/5 )