Parse Parens

See:  https://github.com/ucsd-progsys/liquidhaskell/pull/227

Change the parser so that:

1. we **need not** write so many parenthesis, e.g. at function applications.
2. we **can not** write the old 'p ? e1 : e2' format, and must use 'if p then e1 else e2' instead.

All tests pass on goto. This is linked to a corresponding: ucsd-progsys/liquid-fixpoint#38

See the diff below e.g. 'include/GHC/List.lhs' to see the new format. In brief we can write specs like:

    len v = len x + 1

or

    len v = 2 * len x - 1

It parses "-   1" as an integer token and hence, with the new paren-less funapp, "x - 1" got parsed as "x(-1)" ...

> On Jul 15, 2014, at 11:15 AM, Eric Seidel <notifications@github.com> wrote:
> 
> In src/Language/Fixpoint/Parse.hs:
> 
> > @@ -131,13 +133,22 @@ whiteSpace    = Token.whiteSpace    lexer
> >  stringLiteral = Token.stringLiteral lexer
> >  braces        = Token.braces        lexer
> >  double        = Token.float         lexer
> > -integer       = Token.integer       lexer
> > +-- integer       = Token.integer       lexer
> @ranjitjhala what was the issue with the standard integer parser?
> 
> —
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