Recursively nested anonymous structs

[exellian]

Thanks to https://github.com/oooutlk nested anonymous structs are now initially supported.
To fully support nested anonymous-structs, we should allow recursively nested structs:

Structx!{
    items: Vec<T>,
    test: usize,
    products: Structx!{
        name: T1,
        item: Structx! {
            u: usize
        }
    }
};

This currently produces a cannot find type error.

[exellian]

Closing because this issue is automatically resolved in #4