C++17: Bessel functions

C++17 added the following Bessel functions:

regular modified cylindrical Bessel functions 
cyl_bessel_i
cyl_bessel_if
cyl_bessel_il

cylindrical Bessel functions (of the first kind)  
cyl_bessel_j
cyl_bessel_jf
cyl_bessel_jl
  
irregular modified cylindrical Bessel functions 
cyl_bessel_k
cyl_bessel_kf
cyl_bessel_kl
  
spherical Bessel functions (of the first kind) 
sph_bessel
sph_besself
sph_bessell

References:
https://en.wikipedia.org/wiki/C%2B%2B17
http://en.cppreference.com/w/cpp/numeric/special_math