Statistical Math functions
Statistical Math functions

Adds support for the following statistical and general math functions:
* powi
* sqrt
* exp (exponential function)
* norm_cdf (cumulative distribution of a normal function)
* norm_pdf (Normal probability density function)
* ln (natural logarithm)
* erf (error function)

I'm definitely not a math expert, so critique is welcome!

paupino/rust-decimal,paupino/rust-decimal