Added golden tests using the Diff library

This seems to work. Note that due to a restrictive type signature of `ppDiff` in `Data.Algorithm.DiffOutput` function `diffCmp` has to convert the inputs to Haskell Strings, which might hurt performance/memory usage. At this time I'm not sure how hard it would be to adapt `ppDiff` to accept `ByteString`s (or, maybe, any instance of `Show`). I might look into that at a later time. This is for issue #2