Remove the use of macros in kgr::Autocall

[gracicot]

Right now, to use kgr::Autocall with a relatively nice syntax, you must use a macro that expands into kgr::Method with the name of the function present two times.

With C++17, we could define kgr::AutoCall a bit like that:

template<auto... functions>
struct Autocall {
    // ...
};

[gracicot]

We will need to change kgr::Invoke to be a template variable, since auto only represent non-type template parameter.

[gracicot]

kgr::Map would also need to be a variable template to be passed to kgr::AutoCall without defining two classes.