Simplify code

[denniskb]

I'm a fond user of xoroshiro myself and a C++ programmer. Thank you for this great work!

There is a lot of common, redundant code between the simulators generators. Have you ever considered writing a generic, templated master class and then defining individual RNGs as parameterizations of it?

using XoroShrio256PlusPlus = XoroShiro<256, 64, variant::pp>;

[denniskb]

Would be happy to do the refactoring if you think it's worthwhile..

[Reputeless]

I think making generator classes templatized could bring unnecessary complexity for maintainers and misuse of API.
Instead of templatization, identical jump functions can call a common function to remove redundant code. It will reduce LoC by 10～20%. I will try this in the next update.