Simulate simple orthus dataset and priors (for testing)
Arguments
- D
- number of multinomial categories 
- P
- number of dimensions of second dataset Z 
- N
- number of samples 
- Q
- number of covariates (first one is an intercept, must be > 1) 
- use_names
- should samples, covariates, and categories be named 
- true_priors
- should Xi and upsilon be chosen to have mean at true simulated value