Switch to crossbeam-queue for events

[ahomescu]

Use a lock-free queue to store the event list because the event callbacks might be called from inside a signal handler. Most system calls are not safe in that context, so we just spin if the queue is full.

[kkysen]

Did we run into this causing problems? Signal safety is really annoying.

[spernsteiner]

What's left to do here?

Edit: Should I go audit all the functions in the runtime and check exactly which ones need to be signal-safe? Shouldn't be too hard.

@ahomescu, did you already do this / do you still plan to?

[ahomescu]

What's left to do here?

Edit: Should I go audit all the functions in the runtime and check exactly which ones need to be signal-safe? Shouldn't be too hard.

@ahomescu, did you already do this / do you still plan to?

I added a bunch of comments on signal safety, and removed a few potentially unsafe eprintln! calls.