Add "Inverse Error" function

[Former user]

Hello,

I really love SpeedCrunch, I've been using it since ~2011, when I read about it in an argentinean blog (https://tecnovortex.com/speedcrunch-calculadora-multiplataforma/, then called Alt-Tab). It is my go-to calculator program in Linux and Windows, and always reccomend it to my friends and students. I wanted to thank you for keeping its development through all this years.

I wanted to know if your could add the Inverse Error function to SpeedCrunch, as it is related to erf() and erfc() functions. As far as I'm concerned, it is very useful for chemical diffusion problems, and I guess it will be useful to other engineering areas.

Thanks, Ramiro