C++17: elliptic integrals

C++17 added the following elliptic integral functions:

(complete) elliptic integral of the first kind 
comp_ellint_1
comp_ellint_1f
comp_ellint_1l
 
(complete) elliptic integral of the second kind 
comp_ellint_2
comp_ellint_2f
comp_ellint_2l
  
(complete) elliptic integral of the third kind 
comp_ellint_3
comp_ellint_3f
comp_ellint_3l
  
(incomplete) elliptic integral of the first kind 
ellint_1
ellint_1f
ellint_1l
  
(incomplete) elliptic integral of the second kind 
ellint_2
ellint_2f
ellint_2l
  
(incomplete) elliptic integral of the third kind 
ellint_3
ellint_3f
ellint_3l

References:
https://en.wikipedia.org/wiki/C%2B%2B17
http://en.cppreference.com/w/cpp/numeric/special_math
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1422.html