Implemented fatanh,cosh,etox,etoxm1,lognp1,tanh, and twotox

but not ftentox, because this hits a clang bug. Clang 3.5
(and earlier?) wants to optimize pow(10.0, x) to
__exp10(x), but __exp10() doesn't exist in the 10.8 SDK,
so the linker fails. There's probably some simple workaround...