Fixes doxygen issue

[gf712]

Doxygen doesn't seem to like arguments packs and variadic templates and gives an error in these lines of shogun_doxygen.i:

// File: structshogun_1_1type__internal_1_1function__traits_3_01Ret_07F_1_1_5_08_07Args_8_8_8_08_01const_01_4.xml
%feature("docstring") shogun::type_internal::function_traits<
Ret(F::*)(Args...) const > " "; --> ***this line causes an issue****

and

%feature("docstring") shogun::Types< T1, Args... > " ";

This PR tells doxygen to ignore the corresponding C++ code.

[vigsterkr]

i've killed this CI job... coz the windows build would have taken ages :) but it should be fine to merge. i'll merge it as soon as the #4456 is done