Implement special functions

[astralord]

• logarithm of modified Bessel function of the first and second kind

• lower and upper incomplete gamma functions (and their logarithms)

• Marcum-Q and Marcum-P functions

• erfinv and erfcinv

• incomplete beta function

[astralord]

Useful papers
Computation of the Marcum Q-function
Efficient and accurate algorithms for the computation and inversion of the incomplete gamma function ratios
Extended precision computation of the incomplete beta function.pdf