Currently we always need to create a temporal variable to get a config value. And we don't know, was it really initialised.
I added simple callbacks for it. It's not the best what we can reach, but it's pretty limited by [[ http://trac.wildfiregames.com/wiki/CppSupport | CppSupport ]]. So syntax sugar can be added later.
Example of usages:
```lang=cpp
CFG_GET_VAL("...", std::function<void(const bool&)>(
std::bind(&Class::SetProperty, objectPointer, std::placeholders::_1)
));
CFG_GET_VAL("...", std::function<void(const bool&)>([this](const bool& ...) {
objectPointer->SetProperty(...);
}));
```