[boost] [GSOC] Generalized Hypergeometric Functions.

Hi all. I just added a quick and naive implementation of Pade approximation for 1f1 and 2f1 hypergeometric functions based on Luke's book. You can find code here: https://github.com/AntonBikineev/math/blob/hypergeometric/ include/boost/math/special_functions/detail/hypergeometric_pfq_pade.hpp I also want to thank Christopher Kormanyos for many advices and help. Best regards, Anton.