[Gmsh] Feature requeset: asinh

[Nico Schlömer]

Currently, Gmsh has a number of built-in functions, amongst them
trigonometrical functions, their inverses, and hyperbolic functions.
I have an application where I need the inverse of sinh which is not available.
Given the representation

https://en.wikipedia.org/wiki/Hyperbolic_function#Inverse_functions_as_logarithms

I can work around this easily enough, but one may want to add it to
the array of built-in functions for the sake of compleness.

--Nico