Added empty function to the State monad.
Added empty function to the State monad.

sideeffffect/FSharpx.Extras,bryanedds/FSharpx.Extras,fsprojects/FSharpx.Extras,sideeffffect/FSharpx.Extras,bryanedds/FSharpx.Extras,fsprojects/FSharpx.Extras,bryanedds/FSharpx.Extras