Improve getting started experience

[drogue-iot]

Improve getting started experience

[lulf]

I'm going to attempt to improve the experience of writing and running actors as follows:

1. Introduce a spawn_actor! macro to simplify creation and mounting of the actor context + actor:

let address = spawn_actor!(spawner, BUTTON_A, Button::new(board.btn_a));

2. Introduce a actor proc macro to simplify the Actor impl:

#[actor]
impl Actor for MyActor {
    type Message<'m> = MyMessage;
    async fn on_mount<M>(&mut self, address: Address<Self>, inbox: &mut M)
        where M: Inbox<Self>
    {
        loop {
            if let Some(m) = inbox.next().await {
                // ... handle message
            }
        }
    }
}

The purpose of this macro is not to remove all the boilerplate, but rather prepare the actor implementations to require minimal modifications when async traits are fully available in Rust, so that just removing the #[actor] macro (and making the macro a dummy) will allow the code to keep working.

[ctron]

What I guess would help is:

• Add some documentation on the actor model of Drogue Device
  • What is an actor
  • What is the lifecycle? Init, Inbox, ...
  • When to use an actor vs when not to
• A basic tutorial, which builds (step by step) a simple device (like a blinking LED with a push-button that changes its behavior). Maybe pointing to a dedicated GitHub repository, which contains the full code (and only that). Ready to check out, build, and flash on a device we choose (like the microbit).

[ctron]

Ok, after re-checking the docs. I think it already is there.

[lulf]

Improvements:

• Added cargo xtask clone in #244
• Added docs for BSP in #245

Will take a stab at improving the code docs.