parametrize the Hash algorithm

Data/Git/Diff.hs

Data/Git/Monad.hs

Data/Git/Named.hs

Data/Git/Parser.hs

Data/Git/Path.hs

Data/Git/Ref.hs

Data/Git/Repository.hs

Data/Git/Storage.hs

Data/Git/Storage/FileWriter.hs

Data/Git/Storage/Loose.hs

Data/Git/Storage/Object.hs

Data/Git/Storage/Pack.hs

Data/Git/Storage/PackIndex.hs

Data/Git/Types.hs

Data/Git/WorkTree.hs

tests/Repo.hs

tests/Tests.hs