Actor Result support

[longshorej]

I'm unsure whether such a feature is necessary, but filing the issue to gather thoughts.

• The Result type is great for representing errors.
• The ? operator makes it really easy to work with Results.
• Panicking is heavy weight, not a good general purpose error mechanism
• Users may wish to translate Err into an actor failure

Should we have some sugar to support that use-case? Without any explicit feature, the user might employ a pattern like this:

struct MyMsg;

struct MyActor;

impl MyActor {
  fn handle(msg: MyMsg, ctx: &mut ActorContext) -> Result<()> {
    let thing = some_possible_failure(msg)?;
    let other_thing = some_other_thing(&thing);

    Ok(())
  }
}

impl Actor<MyMsg> for MyActor {
  fn receive(&mut self, msg: MyMsg, ctx: &mut ActorContext) {
    match self.handle(msg, ctx) {
      Ok(()) => {}

      Err(e) => {
        ctx.fail(e);
      }
  }

It feels like that would get repetitive quick, but maybe it's fine.