Fully delegate installation to rstantools (#15)
Other minor fixes to pass R CMD check on R devel
Add offset functionality
Add support for random walk year effects with covariates. Thereare a few specific cases where covariates or the random year effect arenot estimable. Examples are:
Import S3 methods from rstantools instead of rstanarm(#5)
Adjust calculation of year index values to better allow formissing time slices