Functional lenses

Based on F# implementation in https://github.com/fsharp/fsharpx see https://github.com/fsharp/fsharpx/blob/master/src/FSharpx.Extras/Lens.fs for the original implementation see http://bugsquash.blogspot.com/2011/11/lenses-in-f.html - Lenses in F# see http://stackoverflow.com/questions/8179485/updating-nested-immutable-data-structures - Stackoverflow question about Updating nested immutable data structures see http://stackoverflow.com/questions/5767129/lenses-fclabels-data-accessor-which-library-for-structure-access-and-mutatio - Haskell libraries for structure access and mutation see http://www.youtube.com/watch?v=efv0SQNde5Q - Functional lenses for Scala by Edward Kmett on YouTube see http://patternsinfp.wordpress.com/2011/01/31/lenses-are-the-coalgebras-for-the-costate-comonad - Lenses are the coalgebras for the costate comonad by Jeremy Gibbons