Added IKAN source code
Added get_global_position method to Node class
Added solve_2_bones method in SkeletonFitting, this method solves
inverse kinematics problema for two bones, where the first joint has
three degrees of freedom and the second one only one.
Added error checking on Skeletonfitting solve_2_bones, still a wip
Added result check in solve_2_bones in SkeletonFitting
solve_2_bones now takes two arguments that indicate which bones are to be solved.
Previously it would only solve for root and first child.
Fixed solve_2_bones to work with any pair of two bones without restrictions.