Find the name of the likelihood approximation used for fitting
find_approximation_name(method, control)the method used to approximate the likelihood. The options
are "Laplace", "AGQ" (the adaptive Gaussian quadrature approximation,
from lme4), "SR" (the sequential reduction approximation)
and "IS" (an importance sampling approximation).
a list of extra parameters controlling the approximation to the likelihood. See 'Details' for more information.
a string with the name of the likelihood approximation