xmas-party: gamma & beta implementations from obsolete rand package

[thekondor]

Because rand to be dropped soon. Once we are done with this change, we could switch bm to use go-xorshift completely.

[gburanov]

where will other parts in rand will go? For example
https://github.com/remerge/rand/blob/master/gaussian.go
https://github.com/remerge/rand/blob/master/normal.go

[thekondor]

@gburanov they are not used across the remaining repositories. Why do we need to keep them?

[gburanov]

ok, my idea was that even if we are not using them, they belong here (they are also distributions)....

Also I do not really like the package name - it assumes we use xorshift for randomization, but this is just one of the strategies ...

What do you think of opposite approach? Move all the things from here to rand?

I think it will be more clear... WDYT?

[dynamix]

go-xorshift exists because it extracted the random number generator from remerge/rand (+ the lock free UUIDs/URIs) . It should only that. Other libraries like remerge/rand can use it and still include the distributions.

Please keep in mind that this is a public repo :-) i.e. I used it in some none remerge random tests.

[thekondor]

@dynamix since rand is public, looks like that doesn't have any sense to remove any part of it at all, because this can break someone's dependency. Though xorshift is mostly a superset of rand package (except ones mentioned by @gburanov).