Cannot express a truncated uniform prior over missing values in BSR

[Víctor de Buen Remiro]

Now missing values accept prior with scalar distribution normal, truncated normal and pure non informative (no prior).
Adding truncated uniform prior we could use it to simulate censored data.
This feature should be used carefully over input missing due it could give a non regular regression matrix if there are simultaneous input missing without normal or truncated normal prior.