implemented Flip

[leandromoh]

resolved issue #183

[louthy]

@leandromoh Hi Leandro, just to let you know that I haven't forgotten about your pull requests. I have a ton of work to do to get the project stable again after moving to VS2017. Once completed, I'll be reviewing your reqs.

[leandromoh]

@louthy no problem. thanks for the explanation

[louthy]

@leandromoh Hi Leandro, I have modified this. In Haskell flip works on two arguments only. There is a clear reason for that which is composition and application. It's less important in C# as I mentioned in the original issue. However I see a value in flipping the first and the last argument. Especially if C# gets the forward pipe operator that is currently a proposal on Rosyln. However beyond 3 arguments I think flipping the first and the last argument feels wrong. So I have modified this to only work on:

    Func<A, Func<B, R>>           ---> Func<B, Func<A, R>>
    Func<A, Func<B, Func<C, R>>>  ---> Func<C, Func<B, Func<A, R>>>

    Func<A, B, R>                 ---> Func<B, A, R>
    Func<A, B, C, R>              ---> Func<C, B, A, R>

There's a nice symmetry with 2 or 3 arguments which doesn't exist with more.

You can find it here