In windows libuv does not return -errno, instead it uses negative
error codes e.g. UV_ENOENT. This commit changes the comments in os_*
functions to reflect this.
- Improve the implementation of deferred/immediate events.
- Use the new queue module to change how/when events are queued/processed by
giving a private queue to each emitter.
- Immediate events(which only exist to break uv_run recursion) are now
represented in the `loop->fast_events` queue.
- Events pushed to child queues are propagated to the event loop main queue and
processed as K_EVENT keys.
