Create Product Type for each algorithm

[piu130]

We should create a product type for each algorithm.

Example:

-- the function signature
sha256 : String -> String
-- becomes
sha256 : String -> SHA256 String  -- maybe we could also use ByteString later
-- or
sha256 : String -> SHA256 -- with hard-coded String type

So we can switch our functions:

-- from
ineedsha256 : String -> Whatever
-- to
ineedsha256 : SHA256 -> Whatever

There were many bugs because of untyped cryptography in the past and we should not make the same mistake with the nice typed programming language elm.