Seed the generator

[aloisdg]

Hi!

I think for testing purpose, being able to seed the randomization could be useful. This would help fix issue raised on #83

The Random logic is in next and was based on a snippet by @tpetricek

    static member private next =
        let seedGenerator = Random()

        let localGenerator =
            new ThreadLocal<Random>(fun _ ->
                lock
                    seedGenerator
                    (fun _ ->
                        let seed = seedGenerator.Next()
                        Random(seed)))

        fun n -> localGenerator.Value.Next(n)

Random() can be seeded by passing a parameter Random(seed).

Cheers,