BernoulliLogit for Bernoulli{<:LogisticLink}

[theogf]

@devmotion Would that be okay to copy the code of BernoulliLogit and BinomialLogit from Turing to have a special case on Bernoulli{<:LogisticLink} ?

[devmotion]

I think it would be better to move it to Distributions. Most (all?) of these custom distributions should be moved upstream I guess.