Coarse timer for when you don't need a completely accurate clock.
test get_time::slack_500ms ... bench: 1 ns/iter (+/- 0)
test get_time::slack_50ms ... bench: 1 ns/iter (+/- 0)
test get_time::slack_5ms ... bench: 1 ns/iter (+/- 0)
test get_time::stdlib ... bench: 52 ns/iter (+/- 37)
test get_time::through_arc_50ms ... bench: 1 ns/iter (+/- 0)
test now::slack_500ms ... bench: 2 ns/iter (+/- 1)
test now::slack_50ms ... bench: 3 ns/iter (+/- 2)
test now::slack_5ms ... bench: 3 ns/iter (+/- 2)
test now::stdlib ... bench: 757 ns/iter (+/- 232)
test now::through_arc_50ms ... bench: 3 ns/iter (+/- 2)
test now_utc::slack_500ms ... bench: 3 ns/iter (+/- 4)
test now_utc::slack_50ms ... bench: 3 ns/iter (+/- 2)
test now_utc::slack_5ms ... bench: 3 ns/iter (+/- 1)
test now_utc::stdlib ... bench: 214 ns/iter (+/- 48)
test now_utc::through_arc_50ms ... bench: 3 ns/iter (+/- 1)