executor: add spawner

[Keruspe]

This allows spawning a task on an executor from outside of it

Fixes #1

[ghost]

Would this also need the LocalSpawner counterpart?

Perhaps instead of Task::<()>::spawner() it would make more sense to have Spawner::get() or Spawner::current() :)

Does this really require changes to multitask? We could have:

pub struct Executor {
    ex: Arc<multitask::Executor>,
}

pub struct Spawner {
    ex: Arc<multitask::Executor>,
}

[Keruspe]

Sure, don't know why I didn't sync of the Arc version :)

I did the Task::spawner to be symmetrical with Task::spawn but Spawner::current() looks a lot like the Handle::current() from tokio, fine by me

[ghost]

Another argument for current() is that it matches https://doc.rust-lang.org/nightly/std/thread/fn.current.html

[Keruspe]

Wrt the LocalSpawner counterpart, I'm not sure if that's necessary. We can add it for symmetry, but if you want to spawn something on the local executor, thus on the current thread, there's a huge change you're already in it right?

[ghost]

Just minor nits...

[ghost]

I guess you're right, LocalSpawner would be kind of useless :)

[Keruspe]

Fixed the comments

[ghost]

Thanks!

[ghost]

Published in v0.1.2

[Keruspe]

Thanks!

Do you think smol will reexport this or will this stay in the async_executor namespace?

[ghost]

I think it will stay.