Added function for sampling the shape and scale of gamma from their posterior
Added function for sampling the scale of gamma from its posterior, when shape is known
Added function for sampling the shape of gamma from its posterior, when scale is known
Corrected typo
Do not present nbinom2 as an option anymore
Corrected typo
Fixed Poisson model
Poisson model now works in the presence of replicas (although the negative binomial model should be used in this case)