TANH function consumes a floating point number from the top of the stack and pushes back its hyperbolic tangent.
The parameter is considered to be in radians.
Since 2.6.0, this function can be applied to a list of numeric values. In this case, the function is applied to each element of the list thus returning a list.
Since 2.7.1, this fonction can be also applied to a GTS. In this case, the function is applied to each value of the given GTS, returning a new GTS.