feat: Update to std futures

[Marwes]

Updates all dependencies, including futures and tokio to support
std::future::Future. I tried to do as few changes as possible so there is very little async await used (not very idiomatic).

BREAKING CHANGE

[softprops]

@Marwes thank you for taking another stab at this. I'll take a look.

I find the easiest place to start looking more idiomatic is in the example main fns

going from examples that look like this

fn main()  {
  let _ = runtime.block_on(somefuture)
  let _ = runtime.block_on(some_other_future)
}

to examples that look like this

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
  let _ = somefuture.await?;
  let _ = some_other_future.await?;
}

This doesn't need to be a blocker and I could follow up on that if you'd like

[Marwes]

I mainly wanted to get rid of the futures-0.1/tokio-0.1 dependencies. Anything beyond that can be done later.

[softprops]

I can dig it