#6 Add inverse hyperbolic functions

[loserpenguin15]

arcsinh x = ln (x + sqrt(x^2 + 1))
arccosh x = ln (x + sqrt(x^2 - 1)) : x >= 1
and so on...
http://en.wikipedia.org/wiki/Hyperbolic_function#Inverse_functions_as_logarithms

I'll do this as soon as I get a working version of CLN (it seemed to have broke when I upgraded to Snow Leopard)