Add xkcd#221 RNG

[giordano]

As suggested in giordano/RandomBasedArrays.jl#4, it'd be useful to implement the standard IEEE-vetted random number generator whose specification is described in xkcd#221. I think it fits very well in this package, it seems very stable. It should also be rather simple to implement.

[rfourquet]

That's an excellent idea! the specification is very clear and unlikely to change. This is a nice project for anyone interested in contributing, which I'm happy to help with.