Timing as of this commit (macOS 10.13.3, MacBook Pro retina 15-inch,
mid 2015, default loop impls):

| Benchmark                              | 27_queue_master | 27pypy_queue_master             | 36_queue_master              | 37_queue_master              |
|----------------------------------------|-----------------|---------------------------------|------------------------------|------------------------------|
| bench_unbounded_queue_noblock          | 2.09 us         | 10.8 ns: 193.75x faster (-99%)  | 1.34 us: 1.56x faster (-36%) | 1.24 us: 1.69x faster (-41%) |
| bench_bounded_queue_noblock            | 2.55 us         | 10.9 ns: 234.91x faster (-100%) | 1.67 us: 1.53x faster (-35%) | 1.55 us: 1.65x faster (-39%) |
| bench_bounded_queue_block              | 36.1 us         | 2.28 us: 15.81x faster (-94%)   | not significant              | 12.9 us: 2.80x faster (-64%) |
| bench_channel                          | 15.4 us         | 1.91 us: 8.03x faster (-88%)    | 9.96 us: 1.54x faster (-35%) | 8.17 us: 1.88x faster (-47%) |
| bench_bounded_queue_block_hub          | 13.6 us         | 1.07 us: 12.64x faster (-92%)   | 8.61 us: 1.57x faster (-36%) | 7.66 us: 1.77x faster (-44%) |
| bench_channel_hub                      | 7.55 us         | 760 ns: 9.94x faster (-90%)     | 5.11 us: 1.48x faster (-32%) | 4.33 us: 1.75x faster (-43%) |
| bench_unbounded_priority_queue_noblock | 5.02 us         | 186 ns: 26.97x faster (-96%)    | 1.63 us: 3.08x faster (-68%) | 1.60 us: 3.14x faster (-68%) |
| bench_bounded_priority_queue_noblock   | 5.48 us         | 183 ns: 29.91x faster (-97%)    | 1.98 us: 2.77x faster (-64%) | 1.79 us: 3.07x faster (-67%) |

[skip ci]