summarise.lincomb: Compute the posterior distribution for a linear combination of the covariates
from the linear predictor.
Description
This function takes in a CARBayes model object and computes the posterior
distribution and posterior quantiles of a linear combination of the covariates
from the linear predictor. For example, if a quadratic effect of a covariate on
the response was specified, then this function allows you to compute the posterior
distribution of the quadratic relationship.