static random-number generator 'defeated' by seed in constructor

[mmurrian]

Every construction of an EigenMultivariateNormal instance re-seeds the static random-number generator. This will cause all instances to reset their RNG sequence back to the same output whenever a new EigenMultivariateNormal is created. If samples() is only called once per instance, the output is always the same!

I recommend providing a static setSeed(...) function that the user can explicitly call and not setting the seed in the constructor.