Add a ButtonState Machine which represents the state of total_size
label, play button, and download button. Also implemented the
update/determine_state function for ButtonState.
Also implemented required generic functions for MediaMachine<X,Y,Z>
that convert it to the desired state.
Instead of having a Wrapper of StateMachinesWrappers, use only the desired
possible states in A new struct with only 1 Wrapper that covers all 3 of
the embeded state machines.
I don't even know if the comment makes any sense. Sorry.
Currently it's required that you take mut self in order to manipulate
the internal state machines. This would not allow passing an Arc/Rc to
a callback since A/Rc<T> only derefs to &T and not T.
The take_mut crate allows the retrieval of ownership if you have a &mut refference
and as long you return T again. So Arc<Mutex<Machine> could work with
callbacks and embed Nested state machies without copying.
