Implement some sugar

[sebastianselander]

It would be cool to be able to write e.g

xs = 0 `Cons` 1 `Cons` Nil ;

or perhaps

not True = False ;
not False = True ;

I have started a module named Desugar.hs earlier this week which we can build upon.
Most sugar should be quite easy to convert, the hard part is defining them in Grammar.cf such that they don't add any conflicts with current rules