Add new Pardos-Gotor subproblems

[PeterBowman]

Previous works explained how to solve Pardos-Gotor (PG) subproblems 1 to 4. In José M. Pardos-Gotor, Screw Theory in Robotics: An Illustrated and Practicable Introduction to Modern Mechanics, CRC Press, 2022 (GH repo), PG5-8 have been introduced and could be included in our C++ library, too (ideally, with tests).