Provides functions to fit linear mixed models
based on convolutions of the generalized Laplace (GL) distribution.
The GL mixed-effects model includes four special cases with normal random
effects and normal errors (NN), normal random effects and Laplace errors (NL),
Laplace random effects and normal errors (LN), and Laplace random effects
and Laplace errors (LL). The methods are described in Geraci and Farcomeni (2020,
Statistical Methods in Medical Research)