Fix documentation of ComplexMath.Asin, Acos and Log

[beutlich]

The input constraints do not hold for complex numbers and seem to have been copy/pasted from the corresponding Real blocks of Blocks.Math. This is what it reads in MSL v3.2.2:

For Asin/Acos:

The absolute values of the elements of the input <code>u</code> need to
be less or equal to one (<b>abs</b>( u ) <= 1).
Otherwise an error occurs.

For Log:

An error occurs if the elements of the input <code>u</code> are
zero or negative.

[AHaumer]

Agree for Asin and Acos, but how should Complex u be negative? abs(u) is always >= 0, ok for abs(u)=0 we have a problem.

[HansOlsson]

Agree for Asin and Acos, but how should Complex u be negative? abs(u) is always >= 0, ok for abs(u)=0 we have a problem.

Well, -1 seems negative, but Modelica.ComplexMath.log(Complex(-1)) is ok - and thus it seems it should be:
An error occurs if the elements of the input <code>u</code> are zero.

Similarly Modelica.ComplexMath.asin(Complex(2,0) actually works - so we don't need any restriction on those.

However, there is another issue (needs a separate ticket for Modelica.Blocks.Math; will open it) - it is a single input and thus I would expect:
Log: An error occurs if the input <code>u</code> is zero.
Asin/Acos: This space intentionally left blank

It is likely that the error in Modelica.Blocks.Math occurred due to Modelica 1->2 change when blocks changed from having vectors to scalars as inputs.