new MLE methods on Bernoulli
declare BernoulliStats as a subtype of SufficientStats
rename fit_mle --> fit for Beta (it is not MLE)
export SufficientStats
new MLE for Binomial
new MLE for Exponential
new MLE for Normal
new MLE for DiscreteUniform
new MLE for Uniform
new MLE for Gamma
improved fallback message for suffstats
Fixed MLE for Geometric (which was incorrect)
new MLE for Geometric
MLE for Laplace distribution tested
MLE for Poisson distribution tested
new MLE for Dirichlet
new MLE for Multinomial
new MLE for MultivariateNormal
increase nsamples in testing of MLE for MultivariateNormal
relax the criteria in isprobvec