Improve numerical stability in vineFit.

Return finite approximations in the normal and t copula loglik function calls with rho in {-1, 1}.
Set package license as GPL (>= 2).
Update the local copy of the LICENSE file.
Set version number to 1.1.0.
Improve numerical stability of the h-functions of the normal and t copulas.
Reformate code in CITATION file.
Update the NEWS file.