* timer: restructure feature flags
* update timer tests
* Add `async-traits` to CI
This also disables a buggy `threadpool` test. This test should be fixed in the future.
Refs #1225
This patch adds a `DelayQueue` to tokio_timer. The `DelayQueue` allows
inserting elements as well as specifying a time at which the element
should be returned to the user. This allows handling more complex
timeout situations.