A Haskell version

Here is a Haskell version. I more or less translated the F# version
line by line, but used different functions where it made sense for
Haskell.
 
    $ cd ClassifyDigits
    $ cabal install --dependencies-only
    $ cabal build
    $ time dist/build/ClassifyDigits/ClassifyDigits

I don't know how to get the OCaml or F# ones to compile, so I don't
know how it compares in speed to the others. 

On my `Intel(R) Core(TM) i7-3740QM CPU @ 2.70GHz`, the first version completes in 21 seconds on my laptop:

    $ time dist/build/ClassifyDigits/ClassifyDigits
    Start ...
    Percentage correct: 94.39999999999999

    real 0m21.625s
    user 0m21.284s
    sys  0m0.316s

I added some commits showing simple updates I did. With the unboxed vectors version it completes in 6 seconds:

    $ time dist/build/ClassifyDigits/ClassifyDigits
    Start ...
    Percentage correct: 94.39999999999999

    real 0m6.237s
    user 0m6.128s
    sys  0m0.084s