MinFinder rebased PR

Sorry for duplication of #72, but I'm still learning git and could not for the life of me rebase/merge that branch, so out of frustration I created a new one.

In addition to the remarks in #72, I've added Distributions back in because the stopping rule draws from a binomial. If you have some strong feelings about depending on Distributions, I guess I could just implement that here in Optim.jl.

Again, sorry for the duplication, bear with me in my learning curve :)
You may use ``StatsBase.rand_binom`` here, so that you don't have to depend on ``Distributions``. 

Still, such a criterion feels a little weird to me. I may want to look at the paper as to why it is in this way.