Correlated observations that aren't normal

[spinkney]

Feature request: copulas for multivariate responses of mixed types

@tarheel did most of the heavy lifting. I just packaged it up with a bow. Here’s the discrete-continuous multi-variate gaussian case. It uses the truncated MVN to derive the bounds from the latent continuous margins needed for the discrete margins. It’s in PR status but you can check it out at added mixed_copula by spinkney · Pull Request #13 · spinkney/helpful_stan_functions (github.com) You should be able to add gaussian, bernoulli, and poisson or leave any one of those out and the code sho…