Methods to compute extract different features of the log-likelihood function
# S3 method for mhurdle
estfun(x, ...)# S3 method for mhurdle
bread(x, ...)
# S3 method for mhurdle
llcont(x, ...)
a model fitted with mhurdle
further arguments, currently unused
mhurdle exports the sandwich::estfun,
sandwich::bread and nonnest2::llcont functions. The
specific method provided for mhurdle objects are used in the
code to extract different features of the log-likelihood