Feature/add integersequenceentry

The traits class IntegerSequenceEntry computes the i-th entry of an std::integer_sequence. The integerSequenceEntry helper function does the same with function syntax.

This allows to avoid the hight template instantiation depth of std::make_tuple when using the "natural" implementation

std::get<index>(std::make_tuple(t...));

The latter adds 15 instantiation levels per argument whereas the still recursive implementation in this MR adds only one.