We need a possibility to invoke rust functions from the QML side. In traditional Qt/QML these are functions marked as Q_INVOKABLE or Q_SLOTS.

The currently suggested API is to use an attribute of the form

#[qslot(cpp_name = "cppName")]
fn some_function(&mut self, ...) {
    ...
} 

The function can be called with cppName from the QML side (Maybe remove cpp from the name?).

The function should be callable with common standard and Qt types as parameters.

We probably have to also make const qslots work.