This is the fork of the libfgsb3 from cran with the following
differences: - The return type has changed is is very similar to what
optim returns - Allows a direct C/C++ interface through a R
registered function, similar to C interface to optim with 2
additional arguments. - Allows adjustment of tolerances for minimization
success. - Added xtolAtol and xtolRtol
minimization success criterion. - Added maxit
termination