Implement lambda-case/lambda-if

I put together a patch for this Haskell' proposal (http://hackage.haskell.org/trac/haskell-prime/ticket/41)

    Prelude> (if then "Haskell" else "Cafe") False
    "Cafe"
    Prelude> (case of 1 -> "One"; _ -> "Not-one") 1
    "One"

There seems to be some support for integrating this proposal into GHC (see http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/81366)

The attached patches implement the feature, test it and document it.

See also the wiki page LambdasVsPatternMatching.