Vendor dependencies for 0.3.0 release

vendor/tracing/benches/enter_span.rs

@@ -0,0 +1,16 @@
+use criterion::{criterion_group, criterion_main, Criterion};
+use tracing::{span, Level};
+
+mod shared;
+
+fn bench(c: &mut Criterion) {
+    shared::for_all_dispatches(&mut c.benchmark_group("enter_span"), |b| {
+        let span = span!(Level::TRACE, "span");
+        b.iter(|| {
+            let _span = span.enter();
+        })
+    });
+}
+
+criterion_group!(benches, bench);
+criterion_main!(benches);